ci: implement stale issue and pr policy (issue #119)

.github/workflows/stale.yml

@@ -0,0 +1,26 @@
+name: Close stale issues and PRs
+
+on:
+  schedule:
+    - cron: '30 1 * * *'
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+    steps:
+      - uses: actions/stale@v9
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          stale-issue-message: 'This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 7 days.'
+          stale-pr-message: 'This PR is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 7 days.'
+          close-issue-message: 'This issue was closed because it has been stalled for 7 days with no activity.'
+          close-pr-message: 'This PR was closed because it has been stalled for 7 days with no activity.'
+          days-before-stale: 60
+          days-before-close: 7
+          stale-issue-label: 'stale'
+          stale-pr-label: 'stale'
+          exempt-issue-labels: 'bug,enhancement,security,pinned'
+          exempt-pr-labels: 'dependencies,wip'