feat(project): Add cronjob to check for stale issues (#287)

GitHub actions is a workflow engine.
The stale workflow helps us to keep the issue tracker up to date.
Issues that doesn't have activity since 60 days will be marked as
stale and closed eventually.

.github/workflows/stale.yml

@@ -0,0 +1,19 @@
+name: "Close stale issues"
+on:
+  schedule:
+  - cron: "0 4 * * *"
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/stale@v1.1.0
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        stale-issue-message: >
+          This issue has been automatically marked as stale because it has not had
+          recent activity in the last 60 days. It will be closed in 7 days if no further activity occurs.
+          Thank you for your contributions.
+        days-before-stale: 60
+        days-before-close: 7
+        stale-issue-label: stale