Add a github workflow that marks issues and PRs as stale.

PiperOrigin-RevId: 563136967

.github/workflows/stale.yml

@@ -0,0 +1,27 @@
+name: Mark stale issues and pull requests
+
+# Please refer to https://github.com/actions/stale/blob/master/action.yml
+# to see all config knobs of the stale action.
+
+on:
+  schedule:
+  - cron: "0 0 * * *"
+
+jobs:
+  stale:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/stale@v5
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        stale-issue-message: 'A friendly reminder that this issue had no activity for 120 days.'
+        stale-pr-message: 'A friendly reminder that this PR had no activity for 120 days.'
+        stale-issue-label: 'stale-issue'
+        stale-pr-label: 'stale-pr'
+        days-before-stale: 120
+        days-before-close: 540
+        remove-stale-when-updated: true
+        exempt-pr-labels: 'no-auto-close'
+        exempt-issue-labels: 'no-auto-close,new feature,enhancement'