Add stale bot

.github/workflows/stalebot.yml

@@ -0,0 +1,27 @@
+name: "Close stale pull requests"
+on:
+  schedule:
+    - cron: "0 0 * * *"
+
+permissions:
+  contents: read
+
+jobs:
+  stale:
+    permissions:
+      issues: write # for actions/stale to close stale issues
+      pull-requests: write # for actions/stale to close stale PRs
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          stale-pr-message: >
+            This pull request has been automatically marked as stale because it
+            has not had any recent activity. It will be closed if no further
+            activity occurs. Thank you!
+          days-before-stale: -1
+          days-before-close: -1
+          days-before-pr-stale: 8
+          days-before-pr-close: 3
+          exempt-pr-labels: "security, proposal, blocked"