Add stale GitHub Action

.github/workflows/maintenance.yml

@@ -0,0 +1,28 @@
+name: "Close stale issues and pull requests"
+on:
+  schedule:
+  - cron: "0 0 * * *"
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/stale@v1
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        stale-issue-message: >
+          This issue has been open 180 days with no activity. Consequently, it
+          is being marked with the "stale" label. This means is that the issue will be
+          automatically closed in 30 days unless more comments are added or the "stale"
+          label is removed. Comments that provide new information on the issue are
+          especially welcome: is it still reproducible? did it appear in other contexts?
+          how critical is it?
+        stale-pr-message: >
+          This PR has been open 180 days with no activity. Consequently, it
+          is being marked with the "stale" label. This means is that the PR will be
+          automatically closed in 30 days unless more comments are added, code is updated,
+          or the "stale" label is removed.
+        days-before-stale: 180
+        days-before-close: 30
+        stale-issue-label: 'stale'
+        stale-pr-label: 'stale'