ci: add breaking changes auto labeling action

Automatically add/remove `breaking changes` label to PRs as needed based on whether
the PR contains a commit with a breaking change.

(cherry picked from commit d8dbdba)

Author: josephperrott

.github/workflows/dev-infra.yml

@@ -0,0 +1,14 @@
+name: DevInfra
+
+on:
+  pull_request_target:
+    types: [opened, synchronize, reopened]
+
+jobs:
+  breaking-changes-label:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: angular/dev-infra/github-actions/breaking-changes-label@861dc90572784e714aeaa9dfb20ceebeb57cdb07
+        with:
+          angular-robot-key: ${{ secrets.ANGULAR_ROBOT_PRIVATE_KEY }}