Add workflow to close stale issues

.github/workflows/stale.yml

@@ -0,0 +1,18 @@
+name: Close inactive issues
+on:
+  schedule:
+    - cron: "30 0 * * *"
+
+jobs:
+  close-issues:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v3
+        with:
+          days-before-stale: 90
+          days-before-close: 14
+          stale-issue-label: "stale"
+          stale-pr-message: "This PR is stale because it has been open for 90 days with no activity."
+          close-pr-message: "This PR was closed because it has been inactive for 14 days since being marked as stale."
+          stale-issue-message: "This issue is stale because it has been open for 90 days with no activity."
+          close-issue-message: "This issue was closed because it has been inactive for 14 days since being marked as stale."