Add stale workflow to automatically close stale issues and PRs

Signed-off-by: Tsuyoshi Hombashi <tsuyoshi.hombashi@gmail.com>

.github/workflows/stale.yml

@@ -0,0 +1,16 @@
+name: 'Close stale issues and PR'
+on:
+  schedule:
+    - cron: '30 1 * * *'
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          stale-issue-message: 'This issue is stale because it has been open 15 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.'
+          days-before-stale: 15
+          days-before-close: 7
+          only-labels: 'invalid,needs-info,wontfix'