SONARJAVA-5168 Add automation to mark and close stale PRs (#4920)

Author: johann-beleites-sonarsource

.github/workflows/mark-prs-stale.yml

@@ -0,0 +1,20 @@
+name: 'Close stale PRs'
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '30 2 * * *'
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+    steps:
+      - uses: actions/stale@v9
+        with:
+          stale-pr-message: 'This PR is stale because it has been open 7 days with no activity. If there is no activity in the next 7 days it will be closed automatically'
+          stale-pr-label: 'stale'
+          days-before-stale: 7
+          days-before-close: 7
+          exempt-pr-labels: 'do-not-close,External Contribution'