feat: add stale issue and PR management workflow (#89)

* feat: add stale issue and PR management workflow

* chore: add comments

* fix: update comments by the way

* fix: update stale PR messages for consistency

* fix: revert pr template changes

Author: Ki-Seki

.github/workflows/stale.yml

@@ -0,0 +1,27 @@
+name: "Mark stale issues and PRs"
+
+on:
+  schedule:
+    - cron: '0 2 * * *' # Runs every day at 2 AM UTC
+
+permissions:
+  issues: write
+  pull-requests: write
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          stale-issue-message: 'This issue has been automatically marked as stale due to inactivity.'
+          stale-pr-message: 'This PR has been automatically marked as stale due to inactivity.'
+          close-issue-message: 'This issue has been automatically closed due to inactivity.'
+          close-pr-message: 'This PR has been automatically closed due to inactivity.'
+          days-before-stale: 30  # Days of inactivity before marking as stale
+          days-before-close: 7  # Days of inactivity before closing stale issues/PRs
+          stale-issue-label: 'stale'
+          stale-pr-label: 'stale'
+          exempt-issue-labels: 'do not close'
+          exempt-pr-labels: 'do not close'
+          remove-stale-when-updated: true