multiregionccl: add a cold start latency test

This commit adds a test which creates an MR serverless cluster and then
boots the sql pods in each region while disallowing connectivity to other
regions. It also simulates latency to make sure the routing logic works
and to provide a somewhat realistic picture of what to expect.

Release note: None

pkg/ccl/multiregionccl/BUILD.bazel

@@ -26,6 +26,7 @@ go_test(
     name = "multiregionccl_test",
     size = "enormous",
     srcs = [
+        "cold_start_latency_test.go",
         "datadriven_test.go",
         "main_test.go",
         "multiregion_system_table_test.go",
@@ -56,6 +57,7 @@ go_test(
         "//pkg/kv/kvclient/kvcoord",
         "//pkg/kv/kvserver",
         "//pkg/roachpb",
+        "//pkg/rpc",
         "//pkg/security/securityassets",
         "//pkg/security/securitytest",
         "//pkg/server",
@@ -81,22 +83,29 @@ go_test(
         "//pkg/testutils",
         "//pkg/testutils/datapathutils",
         "//pkg/testutils/serverutils",
+        "//pkg/testutils/serverutils/regionlatency",
         "//pkg/testutils/skip",
         "//pkg/testutils/sqlutils",
         "//pkg/testutils/testcluster",
         "//pkg/util",
         "//pkg/util/envutil",
         "//pkg/util/leaktest",
         "//pkg/util/log",
+        "//pkg/util/quotapool",
         "//pkg/util/randutil",
         "//pkg/util/syncutil",
+        "//pkg/util/timeutil",
         "//pkg/util/tracing",
         "//pkg/util/tracing/tracingpb",
         "//pkg/util/uuid",
         "@com_github_cockroachdb_apd_v3//:apd",
         "@com_github_cockroachdb_datadriven//:datadriven",
         "@com_github_cockroachdb_errors//:errors",
+        "@com_github_jackc_pgx_v4//:pgx",
+        "@com_github_stretchr_testify//assert",
         "@com_github_stretchr_testify//require",
+        "@org_golang_google_grpc//:go_default_library",
+        "@org_golang_x_sync//errgroup",
     ],
 )