Add stale issue/pr tracker, remove code-review workflow (slackhq#794)

Co-authored-by: Bryan Burkholder <[email protected]>

.github/workflows/stale.yaml

@@ -0,0 +1,26 @@
+
+# Closes stale issues and PRs
+# https://github.com/marketplace/actions/close-stale-issues
+
+name: 'Close stale issues and PRs'
+on:
+  schedule:
+    - cron: '30 1 * * *'
+
+permissions:
+  contents: write # only for delete-branch option
+  issues: write
+  pull-requests: write
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/[email protected]
+        with:
+          stale-issue-message: 'This issue is stale because it has been open 180 days with no activity. Remove stale label or comment or this will be closed in 30 days.'
+          days-before-issue-stale: 180
+          days-before-issue-close: 30
+          stale-pr-message: 'This PR is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 3 days.'
+          days-before-pr-stale: 30
+          days-before-pr-close: 3