build: create merge script config for components repo

Adds a merge script config for the components repo.
Additionally, wires up a shorthand Yarn script for merging PRs

merge-config.js

@@ -0,0 +1,41 @@
+module.exports = () => {
+  const {major, minor} = parseVersion(require('./package').version);
+  const patchBranch = `${major}.${minor}.x`;
+  const minorBranch = `${major}.x`;
+
+  return {
+    projectRoot: __dirname,
+    repository: {
+      user: 'angular',
+      name: 'components',
+    },
+    claSignedLabel: 'cla: yes',
+    mergeReadyLabel: 'merge ready',
+    labels: [
+      {
+        pattern: 'target: patch',
+        branches: ['master', patchBranch],
+      },
+      {
+        pattern: 'target: minor',
+        branches: ['master', minorBranch],
+      },
+      {
+        pattern: 'target: major',
+        branches: ['master'],
+      },
+      {
+        pattern: 'target: development-branch',
+        // Merge PRs with the given label only into the target branch that has
+        // been specified through the Github UI.
+        branches: (target) => [target],
+      }
+    ],
+  }
+};
+
+/** Converts a version string into an object. */
+function parseVersion(version) {
+  const [major = 0, minor = 0, patch = 0] = version.split('.').map(segment => parseInt(segment));
+  return {major, minor, patch};
+}

package.json

@@ -41,7 +41,8 @@
     "ownerslint": "ts-node --project scripts/ scripts/ownerslint.ts",
     "tslint": "tslint -c tslint.json --project ./tsconfig.json",
     "stylelint": "stylelint \"src/**/*.+(css|scss)\" --config .stylelintrc.json --syntax scss",
-    "resync-caretaker-app": "ts-node --project scripts scripts/caretaking/resync-caretaker-app-prs.ts"
+    "resync-caretaker-app": "ts-node --project scripts scripts/caretaking/resync-caretaker-app-prs.ts",
+    "merge": "ts-node --project scripts scripts/merge-script/cli.ts --config ./merge-config.js"
   },
   "version": "9.1.3",
   "dependencies": {