introduce stalebot (#1157)

.github/workflows/CI_stale.yml

@@ -0,0 +1,15 @@
+name: 'Stalebot'
+on:
+  schedule:
+    - cron: '30 1 * * *'
+
+jobs:
+  makestale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          any-of-labels: 'community-triage'
+          stale-pr-message: 'This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 10 days.'
+          days-before-stale: 30
+          days-before-close: 10