chore: replace stale workflow with probot

.github/workflows/stale.yml

@@ -1,21 +0,0 @@
-name: 'Handle stale issues and PRs'
-on:
-  schedule:
-    - cron: '0 0 * * *'
-  workflow_dispatch:
-
-jobs:
-  stale:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/stale@v3
-        with:
-          repo-token: ${{ secrets.GITHUB_TOKEN }}
-          stale-issue-message: 'This issue is being marked as "stale" because it has been open 20 days with no activity. Remove the "stale" label or comment, otherwise this will be closed in 5 days.'
-          stale-issue-label: 'status: stale'
-          exempt-issue-labels: 'status: pinned'
-          stale-pr-message: 'This PR is being marked as "stale" because it has been open 20 days with no activity. Remove the "stale" label or comment, otherwise this will be closed in 5 days.'
-          stale-pr-label: 'status: stale'
-          exempt-pr-labels: 'status: pinned'
-          days-before-stale: 20
-          days-before-close: 5