ci: add a stale workflow

This workflow periodically scans issues and PRs
to mark inactive items stale and close them after continued inactivity.

Based on the rook project's workflow:

https://github.com/rook/rook/blob/master/.github/workflows/stale.yaml

Signed-off-by: Michael Adam <[email protected]>

.github/workflows/stale.yaml

@@ -0,0 +1,46 @@
+# Mark or close stale issues and PRs
+# based on the rook workflow:
+# https://github.com/rook/rook/blob/master/.github/workflows/stale.yaml
+
+name: "Mark or close stale issues and PRs"
+on:
+  schedule:
+    # Run the stalebot every day at 8pm UTC
+    - cron: "00 20 * * *"
+
+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-22.04
+    if: github.repository == 'ceph/ceph-csi-operator'
+    steps:
+      - uses: actions/stale@28ca1036281a5e5922ead5184a1bbf96e5fc984e # v9.0.0
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          days-before-issue-stale: 60
+          days-before-pr-stale: 30
+          days-before-close: 7
+          days-before-pr-close: 14
+          stale-issue-message: >
+            This issue has been automatically marked as stale because it has not had recent activity.
+            It will be closed in a week if no further activity occurs.
+            Thank you for your contributions.
+          stale-pr-message: >
+            This pull request has been automatically marked as stale because it has not had
+            recent activity. It will be closed in two weeks if no further activity occurs.
+            Thank you for your contributions.
+          close-issue-message: >
+            This issue has been automatically closed due to inactivity.
+            Please re-open if this still requires investigation.
+          close-pr-message: >
+            This pull request has been automatically closed due to inactivity.
+            Please re-open if these changes are still required.
+          stale-pr-label: "stale"
+          stale-issue-label: "wontfix"
+          exempt-issue-labels: "keepalive,security,reliability"
+          exempt-pr-labels: "keepalive,security,reliability"