github: introduce actions/stale for handling issues/PRs (#391)

Signed-off-by: Kentaro Hayashi <hayashi@clear-code.com>

.github/workflows/stale-actions.yml

@@ -0,0 +1,29 @@
+name: "Mark or close stale issues and PRs"
+on:
+  schedule:
+  - cron: "00 11 * * *"
+
+permissions: read-all
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+    steps:
+    - uses: actions/stale@28ca1036281a5e5922ead5184a1bbf96e5fc984e # v9.0.0
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        days-before-stale: 30
+        days-before-close: 7
+        stale-issue-message: "This issue has been automatically marked as stale because it has been open 30 days with no activity. Remove stale label or comment or this issue will be closed in 7 days"
+        stale-pr-message: "This PR has been automatically marked as stale because it has been open 30 days with no activity. Remove stale label or comment or this PR will be closed in 7 days"
+        close-issue-message: "This issue was automatically closed because of stale in 7 days"
+        close-pr-message: "This PR was automatically closed because of stale in 7 days"
+        stale-pr-label: "stale"
+        stale-issue-label: "stale"
+        exempt-issue-labels: "bug,enhancement,help wanted,moreinfo,pending,question,wontfix"
+        exempt-pr-labels: "bug,enhancement,help wanted,moreinfo,pending,question,wontfix"
+        exempt-all-assignees: true
+        exempt-all-milestones: true