Create GitHub workflow to close stale issues (#58)

<!-- Korbit AI PR Description Start -->
## Description by Korbit AI

### What change is being made?

Create a GitHub workflow to automatically mark inactive issues as stale
and subsequently close them if there is no further activity.

### Why are these changes being made?

This workflow is being implemented to manage and streamline the issue
tracking process by reducing clutter from inactive issues, making it
easier for maintainers to focus on active tasks. The automation helps in
maintaining a clean and organized issue backlog, enhancing overall
project management efficiency while ensuring that only relevant and
active issues receive attention.

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commenting `/korbit-generate-pr-description`
<!-- Korbit AI PR Description End -->

.github/workflows/issue_stale.yml

@@ -0,0 +1,22 @@
+name: Stale and close inactive issues
+on:
+  schedule:
+    - cron: "0 1 * * *"
+
+jobs:
+  close-issues:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+    steps:
+      - uses: actions/stale@v9
+        with:
+          operations-per-run: 250
+          exempt-issue-labels: "in progress"
+          days-before-pr-stale: -1
+          days-before-pr-close: -1
+          days-before-issue-stale: 30
+          days-before-issue-close: 5
+          stale-issue-label: "stale"
+          stale-issue-message: "This issue is stale because it has been open for 30 days with no activity."
+          close-issue-message: "This issue was closed because it has been inactive for 5 days since being marked as stale."