Add stale bog

.github/workflows/stale.yml

@@ -0,0 +1,29 @@
+name: stale
+
+on:
+  schedule:
+    - cron: '0 23 * * SUN-THU'
+
+jobs:
+  stale:
+
+    runs-on: ubuntu-latest
+
+    if: github.repository == 'optuna/optuna-dashboard'
+    steps:
+    - uses: actions/stale@v6
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        stale-issue-message: 'This issue has not seen any recent activity.'
+        stale-pr-message: 'This pull request has not seen any recent activity.'
+        close-issue-message: 'This issue was closed automatically because it had not seen any recent activity. If you want to discuss it, you can reopen it freely.'
+        close-pr-message: 'This pull request was closed automatically because it had not seen any recent activity. If you want to discuss it, you can reopen it freely.'
+        days-before-issue-stale: 60  # default number
+        days-before-issue-close: 7  # default number
+        days-before-pr-stale: 60  # default number
+        days-before-pr-close: 7  # default number
+        stale-issue-label: 'stale'
+        stale-pr-label: 'stale'
+        exempt-issue-labels: 'no-stale'
+        exempt-pr-labels: 'no-stale'
+        operations-per-run: 1000