chore(ci): add stale bot workflow for issue and PR management (kubernetes-sigs#642)

This workflow runs daily at 03:17 UTC and can be triggered manually. It:

* Uses **actions/stale\@v9** to manage inactive issues and pull requests.
* Labels issues/PRs as `stale` after **30 days of inactivity**, unless they carry the `keepalive` label.
* Issues are **never auto-closed** (only marked stale).
* PRs are **auto-closed after 60 days** of inactivity, with a notice that they can be reopened.
* Maintainers get hygiene reminders via messages when items go stale.
* Limits processing to 50 items per run and removes stale labels if activity resumes.

Signed-off-by: Jakob Möller <[email protected]>

Author: jakobmoellerdev

.github/workflows/stale-bot.yaml

@@ -0,0 +1,54 @@
+# .github/workflows/stale.yml
+name: Stale Bot
+
+on:
+  schedule:
+    # run daily at 03:17 UTC, to avoid clashing with a lot of other runs on Github CI
+    - cron: '17 3 * * *'
+  workflow_dispatch: # allow manual triggering
+
+permissions:
+  issues: write
+  pull-requests: write
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Run stale action
+        uses: actions/stale@v9
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+
+          # General
+          operations-per-run: 50
+          remove-stale-when-updated: true
+          enable-statistics: true
+
+          # Labels
+          stale-issue-label: stale
+          stale-pr-label: stale
+          exempt-issue-labels: keepalive
+          exempt-pr-labels: keepalive
+
+          # Timing
+          days-before-issue-stale: 30
+          # never auto-close issues
+          days-before-issue-close: -1
+          days-before-pr-stale: 30
+          # auto close PRs after 60 days of inactivity.
+          # Authors can simply reopen the PR when coming back to it.
+          days-before-pr-close: 60
+
+          # Messaging
+          stale-issue-message: >
+            This issue has been marked **stale** due to 30 days of inactivity.
+            Maintainers use this label for hygiene. 
+            Comment or add a relevant label (keepalive) to keep it from becoming stale.
+          stale-pr-message: >
+            This pull request has been marked **stale** due to 30 days of inactivity.
+            Push changes, comment or add a relevant label (keepalive) to keep it from becoming stale.
+            It will be closed in 30 days if no activity occurs.
+          close-pr-message: >
+            Closing this PR due to prolonged inactivity. Feel free to reopen or submit a new PR when coming back to it.
+