close stale PRs and issues on a cadence (#323)

Author: djeebus

.github/workflows/nightly.yaml

@@ -0,0 +1,18 @@
+name: maintenance
+
+on:
+  schedule:
+    - cron: "0 9 * * 1"   # 9 am on Monday
+
+jobs:
+  clean-up:
+    runs-on: ubuntu-22.04
+
+    permissions:
+      issues: write
+      pull-requests: write
+
+    steps:
+      - uses: actions/stale@v9.0.0
+        with:
+          days-before-stale: '120'