CI: Add cleanup branches cronjob (with dry-run: true) (#111428)

* CI: Add cleanup branches cronjob (with dry-run: true)

* update codeowners

.github/CODEOWNERS

@@ -1262,6 +1262,7 @@ embed.go @grafana/grafana-as-code
 /.github/workflows/changelog.yml @zserge
 /.github/workflows/shellcheck.yml @grafana/grafana-developer-enablement-squad
 /.github/workflows/release-build.yml @grafana/grafana-developer-enablement-squad
+/.github/workflows/cleanup-branches.yml @grafana/grafana-developer-enablement-squad
 /.github/workflows/publish-artifact.yml @grafana/grafana-developer-enablement-squad
 /.github/actions/changelog @zserge
 /.github/workflows/swagger-gen.yml @grafana/grafana-backend-group

.github/workflows/cleanup-branches.yml

@@ -0,0 +1,18 @@
+name: Clean up orphaned branches
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 9 * * 1"
+
+jobs:
+  cleanup-branches:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: read
+    steps:
+      - uses: actions/checkout@v5
+      - uses: grafana/shared-workflows/actions/cleanup-branches@cleanup-branches/v1.0.0
+        with:
+          dry-run: true
+          max-date: "1 month ago"