Send a Slack notification when Repo Sync stalls (#16785)

* Check if Repo Sync has stalled

Co-authored-by: Chiedo <chiedo@users.noreply.github.com>
Co-authored-by: James M. Greene <JamesMGreene@github.com>

Author: chiedo

.github/workflows/repo-sync-stalls.yml

@@ -0,0 +1,58 @@
+name: Repo Sync Stalls
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '*/30 * * * *'
+jobs:
+  check-freezer:
+    name: Check for deployment freezes
+    runs-on: ubuntu-latest
+    steps:
+      - name: Exit if repo is frozen
+        if: ${{ env.FREEZE == 'true' }}
+        run: |
+          echo 'The repo is currently frozen! Exiting this workflow.'
+          exit 1 # prevents further steps from running
+  repo-sync-stalls:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f
+        with:
+          ref: repo-sync
+      - name: Check if repo sync is stalled
+        uses: actions/github-script@626af12fe9a53dc2972b48385e7fe7dec79145c9
+        with:
+          github-token: ${{ secrets.DOCUBOT_FR_PROJECT_BOARD_WORKFLOWS_REPO_ORG_READ_SCOPES }}
+          script: |
+            let pulls;
+            const owner = context.payload.repository.owner.login
+            const repo = context.payload.repository.name
+            try {
+              pulls = await github.pulls.list({
+                owner: owner,
+                repo: repo,
+                head: `${owner}:repo-sync`,
+                state: 'open'
+              });
+            } catch(err) {
+              throw err
+              return
+            }
+
+            pulls.data.forEach(pr => {
+              const timeDelta = Date.now() - Date.parse(pr.created_at);
+              const minutesOpen = timeDelta / 1000 / 60;
+
+              if (minutesOpen > 30) {
+                core.setFailed('Repo sync appears to be stalled') 
+              }
+            })
+      - name: Send Slack notification if workflow fails
+        uses: rtCamp/action-slack-notify@e17352feaf9aee300bf0ebc1dfbf467d80438815
+        if: ${{ failure() }}
+        env:
+          SLACK_WEBHOOK: ${{ secrets.DOCS_ALERTS_SLACK_WEBHOOK }}
+          SLACK_USERNAME: docs-repo-sync
+          SLACK_ICON_EMOJI: ':ohno:'
+          SLACK_COLOR: '#B90E0A' # Crimson
+          SLACK_MESSAGE: Repo sync appears to be stalled for ${{github.repository}}. See https://github.com/${{github.repository}}/pulls?q=is%3Apr+is%3Aopen+repo+sync