Add workflow that comments when PRs include the add to what's new label (#99637)

Co-authored-by: Mitch Seaman <mjseaman@users.noreply.github.com>

.github/CODEOWNERS

@@ -743,6 +743,7 @@ embed.go @grafana/grafana-as-code
 /.github/pr-checks.json @tolzhabayev
 /.github/pr-commands.json @tolzhabayev
 /.github/renovate.json5 @grafana/frontend-ops
+/.github/workflows/add-to-whats-new.yml @grafana/docs-tooling
 /.github/workflows/auto-triager/ @grafana/plugins-platform-frontend
 /.github/workflows/alerting-swagger-gen.yml @grafana/alerting-backend
 /.github/workflows/auto-milestone.yml @grafana/grafana-developer-enablement-squad

.github/workflows/add-to-whats-new.yml

@@ -0,0 +1,16 @@
+name: Add comment about adding a What's new note
+on:
+  pull_request:
+    types: [labeled]
+
+jobs:
+  add-comment:
+    if: ${{ ! github.event.pull_request.head.repo.fork && contains(github.event.pull_request.labels.*.name, 'add to what''s new') }}
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    steps:
+      - uses: marocchino/sticky-pull-request-comment@52423e01640425a022ef5fd42c6fb5f633a02728 # v2.9.1
+        with:
+          message: |
+            Since you've added the `Add to what's new` label, consider drafting a [What's new note](https://admin.grafana.com/content-admin/#/collections/whats-new/new) for this feature.