ci: add stale workflow

.github/workflows/stale.yml

@@ -0,0 +1,24 @@
+name: Stale
+
+permissions:
+  issues: write
+  pull-requests: write
+
+on:
+  workflow_dispatch:
+  schedule:
+    # At 08:00 on every Monday.
+    - cron: "0 8 * * 1"
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          days-before-pr-stale: 180
+          days-before-pr-close: 14
+          stale-pr-message: "This PR has been open for **180 days** with no activity. Remove the stale label or add a comment or it will be closed in **14 days**."
+          days-before-issue-stale: 365
+          days-before-issue-close: -1
+          stale-issue-message: "This issue has been open for **365 days** with no activity. Marking as stale."