ci: add auto lock bot

Activate auto lock bot for PRs and issues.

Author: Keen Yee Liau

.github/workflows/lock-closed.yml

@@ -0,0 +1,14 @@
+name: Lock closed inactive issues
+
+on:
+  schedule:
+    # Run at 16:00 every day
+    - cron: '0 16 * * *'
+
+jobs:
+  lock_closed:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: angular/dev-infra/github-actions/lock-closed@66462f6
+        with:
+          lock-bot-key: ${{ secrets.LOCK_BOT_PRIVATE_KEY }}