Workflow for stale issue and PR management (#1125)

https://docs.github.com/en/actions/managing-issues-and-pull-requests/closing-inactive-issues

Manage issues and PRs that are unassigned, and/or don't have the
'good-first-issue' label (for issues).

60 days for a warning, and closure two weeks later.

.github/workflows/staleness.yml

@@ -0,0 +1,23 @@
+name: "Close stale issues and PRs"
+on:
+  schedule:
+    - cron: "0 18 * * *"
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v9
+        with:
+          days-before-stale: 60
+          days-before-close: 14
+          stale-issue-label: stale
+          stale-pr-label: stale
+          remove-stale-when-updated: true
+          exempt-issue-labels: "good first issue"
+          exempt-all-assignees: true
+          ignore-updates: false
+          stale-issue-message: "This issue has not had any activity for 60 days and will be automatically closed in two weeks"
+          stale-pr-message: "This pull request has not had any activity for 60 days and will be automatically closed in two weeks"
+          close-issue-message: "Automatically closing stale issue"
+          close-pr-message: "Automatically closing stale pull request"