feat: deferred client initialization (#370)

This PR includes changes from googleapis/gapic-generator-typescript#317
that will move the asynchronous initialization and authentication from the client constructor
to an `initialize()` method. This method will be automatically called when the first RPC call
is performed.

The client library usage has not changed, there is no need to update any code.

If you want to make sure the client is authenticated _before_ the first RPC call, you can do
```js
await client.initialize();
```
manually before calling any client method.

packages/google-cloud-tasks/synth.metadata

@@ -1,13 +1,13 @@
 {
-  "updateTime": "2020-02-29T12:46:32.088143Z",
+  "updateTime": "2020-03-05T23:17:35.829582Z",
   "sources": [
     {
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         "name": "googleapis",
         "remote": "https://github.com/googleapis/googleapis.git",
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-        "log": "83c6f84035ee0f80eaa44d8b688a010461cc4080\nUpdate google/api/auth.proto to make AuthProvider to have JwtLocation\n\nPiperOrigin-RevId: 297918498\n\ne9e90a787703ec5d388902e2cb796aaed3a385b4\nDialogflow weekly v2/v2beta1 library update:\n  - adding get validation result\n  - adding field mask override control for output audio config\nImportant updates are also posted at:\nhttps://cloud.google.com/dialogflow/docs/release-notes\n\nPiperOrigin-RevId: 297671458\n\n1a2b05cc3541a5f7714529c665aecc3ea042c646\nAdding .yaml and .json config files.\n\nPiperOrigin-RevId: 297570622\n\ndfe1cf7be44dee31d78f78e485d8c95430981d6e\nPublish `QueryOptions` proto.\n\nIntroduced a `query_options` input in `ExecuteSqlRequest`.\n\nPiperOrigin-RevId: 297497710\n\ndafc905f71e5d46f500b41ed715aad585be062c3\npubsub: revert pull init_rpc_timeout & max_rpc_timeout back to 25 seconds and reset multiplier to 1.0\n\nPiperOrigin-RevId: 297486523\n\nf077632ba7fee588922d9e8717ee272039be126d\nfirestore: add update_transform\n\nPiperOrigin-RevId: 297405063\n\n0aba1900ffef672ec5f0da677cf590ee5686e13b\ncluster: use square brace for cross-reference\n\nPiperOrigin-RevId: 297204568\n\n5dac2da18f6325cbaed54603c43f0667ecd50247\nRestore retry params in gapic config because securitycenter has non-standard default retry params.\nRestore a few retry codes for some idempotent methods.\n\nPiperOrigin-RevId: 297196720\n\n1eb61455530252bba8b2c8d4bc9832960e5a56f6\npubsub: v1 replace IAM HTTP rules\n\nPiperOrigin-RevId: 297188590\n\n80b2d25f8d43d9d47024ff06ead7f7166548a7ba\nDialogflow weekly v2/v2beta1 library update:\n  - updates to mega agent api\n  - adding field mask override control for output audio config\nImportant updates are also posted at:\nhttps://cloud.google.com/dialogflow/docs/release-notes\n\nPiperOrigin-RevId: 297187629\n\n0b1876b35e98f560f9c9ca9797955f020238a092\nUse an older version of protoc-docs-plugin that is compatible with the specified gapic-generator and protobuf versions.\n\nprotoc-docs-plugin >=0.4.0 (see commit https://github.com/googleapis/protoc-docs-plugin/commit/979f03ede6678c487337f3d7e88bae58df5207af) is incompatible with protobuf 3.9.1.\n\nPiperOrigin-RevId: 296986742\n\n1e47e676cddbbd8d93f19ba0665af15b5532417e\nFix: Restore a method signature for UpdateCluster\n\nPiperOrigin-RevId: 296901854\n\n7f910bcc4fc4704947ccfd3ceed015d16b9e00c2\nUpdate Dataproc v1beta2 client.\n\nPiperOrigin-RevId: 296451205\n\nde287524405a3dce124d301634731584fc0432d7\nFix: Reinstate method signatures that had been missed off some RPCs\nFix: Correct resource types for two fields\n\nPiperOrigin-RevId: 296435091\n\ne5bc9566ae057fb4c92f8b7e047f1c8958235b53\nDeprecate the endpoint_uris field, as it is unused.\n\nPiperOrigin-RevId: 296357191\n\n8c12e2b4dca94e12bff9f538bdac29524ff7ef7a\nUpdate Dataproc v1 client.\n\nPiperOrigin-RevId: 296336662\n\n17567c4a1ef0a9b50faa87024d66f8acbb561089\nRemoving erroneous comment, a la https://github.com/googleapis/java-speech/pull/103\n\nPiperOrigin-RevId: 296332968\n\n3eaaaf8626ce5b0c0bc7eee05e143beffa373b01\nAdd BUILD.bazel for v1 secretmanager.googleapis.com\n\nPiperOrigin-RevId: 296274723\n\ne76149c3d992337f85eeb45643106aacae7ede82\nMove securitycenter v1 to use generate from annotations.\n\nPiperOrigin-RevId: 296266862\n\n203740c78ac69ee07c3bf6be7408048751f618f8\nAdd StackdriverLoggingConfig field to Cloud Tasks v2 API.\n\nPiperOrigin-RevId: 296256388\n\ne4117d5e9ed8bbca28da4a60a94947ca51cb2083\nCreate a Bazel BUILD file for the google.actions.type export.\n\nPiperOrigin-RevId: 296212567\n\na9639a0a9854fd6e1be08bba1ac3897f4f16cb2f\nAdd secretmanager.googleapis.com v1 protos\n\nPiperOrigin-RevId: 295983266\n\nce4f4c21d9dd2bfab18873a80449b9d9851efde8\nasset: v1p1beta1 remove SearchResources and SearchIamPolicies\n\nPiperOrigin-RevId: 295861722\n\ncb61d6c2d070b589980c779b68ffca617f789116\nasset: v1p1beta1 remove SearchResources and SearchIamPolicies\n\nPiperOrigin-RevId: 295855449\n\nab2685d8d3a0e191dc8aef83df36773c07cb3d06\nfix: Dataproc v1 - AutoscalingPolicy annotation\n\nThis adds the second resource name pattern to the\nAutoscalingPolicy resource.\n\nCommitter: @lukesneeringer\nPiperOrigin-RevId: 295738415\n\n8a1020bf6828f6e3c84c3014f2c51cb62b739140\nUpdate cloud asset api v1p4beta1.\n\nPiperOrigin-RevId: 295286165\n\n5cfa105206e77670369e4b2225597386aba32985\nAdd service control related proto build rule.\n\nPiperOrigin-RevId: 295262088\n\nee4dddf805072004ab19ac94df2ce669046eec26\nmonitoring v3: Add prefix \"https://cloud.google.com/\" into the link for global access\ncl 295167522, get ride of synth.py hacks\n\nPiperOrigin-RevId: 295238095\n\nd9835e922ea79eed8497db270d2f9f85099a519c\nUpdate some minor docs changes about user event proto\n\nPiperOrigin-RevId: 295185610\n\n5f311e416e69c170243de722023b22f3df89ec1c\nfix: use correct PHP package name in gapic configuration\n\nPiperOrigin-RevId: 295161330\n\n6cdd74dcdb071694da6a6b5a206e3a320b62dd11\npubsub: v1 add client config annotations and retry config\n\nPiperOrigin-RevId: 295158776\n\n5169f46d9f792e2934d9fa25c36d0515b4fd0024\nAdded cloud asset api v1p4beta1.\n\nPiperOrigin-RevId: 295026522\n\n56b55aa8818cd0a532a7d779f6ef337ba809ccbd\nFix: Resource annotations for CreateTimeSeriesRequest and ListTimeSeriesRequest should refer to valid resources. TimeSeries is not a named resource.\n\nPiperOrigin-RevId: 294931650\n\n0646bc775203077226c2c34d3e4d50cc4ec53660\nRemove unnecessary languages from bigquery-related artman configuration files.\n\nPiperOrigin-RevId: 294809380\n\n8b78aa04382e3d4147112ad6d344666771bb1909\nUpdate backend.proto for schemes and protocol\n\nPiperOrigin-RevId: 294788800\n\n80b8f8b3de2359831295e24e5238641a38d8488f\nAdds artman config files for bigquerystorage endpoints v1beta2, v1alpha2, v1\n\nPiperOrigin-RevId: 294763931\n\n2c17ac33b226194041155bb5340c3f34733f1b3a\nAdd parameter to sample generated for UpdateInstance. Related to https://github.com/googleapis/python-redis/issues/4\n\nPiperOrigin-RevId: 294734008\n\nd5e8a8953f2acdfe96fb15e85eb2f33739623957\nMove bigquery datatransfer to gapic v2.\n\nPiperOrigin-RevId: 294703703\n\nefd36705972cfcd7d00ab4c6dfa1135bafacd4ae\nfix: Add two annotations that we missed.\n\nPiperOrigin-RevId: 294664231\n\n8a36b928873ff9c05b43859b9d4ea14cd205df57\nFix: Define the \"bigquery.googleapis.com/Table\" resource in the BigQuery Storage API (v1beta2).\n\nPiperOrigin-RevId: 294459768\n\nc7a3caa2c40c49f034a3c11079dd90eb24987047\nFix: Define the \"bigquery.googleapis.com/Table\" resource in the BigQuery Storage API (v1).\n\nPiperOrigin-RevId: 294456889\n\n5006247aa157e59118833658084345ee59af7c09\nFix: Make deprecated fields optional\nFix: Deprecate SetLoggingServiceRequest.zone in line with the comments\nFeature: Add resource name method signatures where appropriate\n\nPiperOrigin-RevId: 294383128\n\neabba40dac05c5cbe0fca3a35761b17e372036c4\nFix: C# and PHP package/namespace capitalization for BigQuery Storage v1.\n\nPiperOrigin-RevId: 294382444\n\nf8d9a858a7a55eba8009a23aa3f5cc5fe5e88dde\nfix: artman configuration file for bigtable-admin\n\nPiperOrigin-RevId: 294322616\n\n0f29555d1cfcf96add5c0b16b089235afbe9b1a9\nAPI definition for (not-yet-launched) GCS gRPC.\n\nPiperOrigin-RevId: 294321472\n\nfcc86bee0e84dc11e9abbff8d7c3529c0626f390\nfix: Bigtable Admin v2\n\nChange LRO metadata from PartialUpdateInstanceMetadata\nto UpdateInstanceMetadata. (Otherwise, it will not build.)\n\nPiperOrigin-RevId: 294264582\n\n6d9361eae2ebb3f42d8c7ce5baf4bab966fee7c0\nrefactor: Add annotations to Bigtable Admin v2.\n\nPiperOrigin-RevId: 294243406\n\nad7616f3fc8e123451c8b3a7987bc91cea9e6913\nFix: Resource type in CreateLogMetricRequest should use logging.googleapis.com.\nFix: ListLogEntries should have a method signature for convenience of calling it.\n\nPiperOrigin-RevId: 294222165\n\n63796fcbb08712676069e20a3e455c9f7aa21026\nFix: Remove extraneous resource definition for cloudkms.googleapis.com/CryptoKey.\n\nPiperOrigin-RevId: 294176658\n\ne7d8a694f4559201e6913f6610069cb08b39274e\nDepend on the latest gapic-generator and resource names plugin.\n\nThis fixes the very old an very annoying bug: https://github.com/googleapis/gapic-generator/pull/3087\n\nPiperOrigin-RevId: 293903652\n\n806b2854a966d55374ee26bb0cef4e30eda17b58\nfix: correct capitalization of Ruby namespaces in SecurityCenter V1p1beta1\n\nPiperOrigin-RevId: 293903613\n\n1b83c92462b14d67a7644e2980f723112472e03a\nPublish annotations and grpc service config for Logging API.\n\nPiperOrigin-RevId: 293893514\n\n"
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+        "internalRef": "299181282",
+        "log": "f0b581b5bdf803e45201ecdb3688b60e381628a8\nfix: recommendationengine/v1beta1 update some comments\n\nPiperOrigin-RevId: 299181282\n\n10e9a0a833dc85ff8f05b2c67ebe5ac785fe04ff\nbuild: add generated BUILD file for Routes Preferred API\n\nPiperOrigin-RevId: 299164808\n\n86738c956a8238d7c77f729be78b0ed887a6c913\npublish v1p1beta1: update with absolute address in comments\n\nPiperOrigin-RevId: 299152383\n\n73d9f2ad4591de45c2e1f352bc99d70cbd2a6d95\npublish v1: update with absolute address in comments\n\nPiperOrigin-RevId: 299147194\n\nd2158f24cb77b0b0ccfe68af784c6a628705e3c6\npublish v1beta2: update with absolute address in comments\n\nPiperOrigin-RevId: 299147086\n\n7fca61292c11b4cd5b352cee1a50bf88819dd63b\npublish v1p2beta1: update with absolute address in comments\n\nPiperOrigin-RevId: 299146903\n\n583b7321624736e2c490e328f4b1957335779295\npublish v1p3beta1: update with absolute address in comments\n\nPiperOrigin-RevId: 299146674\n\n638253bf86d1ce1c314108a089b7351440c2f0bf\nfix: add java_multiple_files option for automl text_sentiment.proto\n\nPiperOrigin-RevId: 298971070\n\n373d655703bf914fb8b0b1cc4071d772bac0e0d1\nUpdate Recs AI Beta public bazel file\n\nPiperOrigin-RevId: 298961623\n\ndcc5d00fc8a8d8b56f16194d7c682027b2c66a3b\nfix: add java_multiple_files option for automl classification.proto\n\nPiperOrigin-RevId: 298953301\n\na3f791827266f3496a6a5201d58adc4bb265c2a3\nchore: automl/v1 publish annotations and retry config\n\nPiperOrigin-RevId: 298942178\n\n01c681586d8d6dbd60155289b587aee678530bd9\nMark return_immediately in PullRequest deprecated.\n\nPiperOrigin-RevId: 298893281\n\nc9f5e9c4bfed54bbd09227e990e7bded5f90f31c\nRemove out of date documentation for predicate support on the Storage API\n\nPiperOrigin-RevId: 298883309\n\nfd5b3b8238d783b04692a113ffe07c0363f5de0f\ngenerate webrisk v1 proto\n\nPiperOrigin-RevId: 298847934\n\n541b1ded4abadcc38e8178680b0677f65594ea6f\nUpdate cloud asset api v1p4beta1.\n\nPiperOrigin-RevId: 298686266\n\nc0d171acecb4f5b0bfd2c4ca34fc54716574e300\n  Updated to include the Notification v1 API.\n\nPiperOrigin-RevId: 298652775\n\n2346a9186c0bff2c9cc439f2459d558068637e05\nAdd Service Directory v1beta1 protos and configs\n\nPiperOrigin-RevId: 298625638\n\na78ed801b82a5c6d9c5368e24b1412212e541bb7\nPublishing v3 protos and configs.\n\nPiperOrigin-RevId: 298607357\n\n4a180bfff8a21645b3a935c2756e8d6ab18a74e0\nautoml/v1beta1 publish proto updates\n\nPiperOrigin-RevId: 298484782\n\n6de6e938b7df1cd62396563a067334abeedb9676\nchore: use the latest gapic-generator and protoc-java-resource-name-plugin in Bazel workspace.\n\nPiperOrigin-RevId: 298474513\n\n244ab2b83a82076a1fa7be63b7e0671af73f5c02\nAdds service config definition for bigqueryreservation v1\n\nPiperOrigin-RevId: 298455048\n\n"
       }
     },
     {