github action: add stales action

Add action to add stale label on issues and PR when no activity
during 45 days.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>

.github/workflows/stales.yml

@@ -0,0 +1,26 @@
+name: 'Stale issues and pull requests with no recent activity'
+on:
+  schedule:
+  - cron: "15 00 * * *"
+
+permissions:
+  issues: write
+  pull-requests: write
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/stale@v4.1.0
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        stale-issue-message: 'This issue has been marked as a stale issue because it has been open (more than) 45 days with no activity.'
+        stale-pr-message: 'This pull request has been marked as a stale pull request because it has been open (more than) 45 days with no activity.'
+        stale-issue-label: Stale
+        stale-pr-label: Stale
+        exempt-issue-labels: bug,enhancement
+        exempt-pr-labels: bug,enhancement
+        days-before-stale: 45
+        remove-stale-when-updated: true
+        remove-issue-stale-when-updated: true
+        remove-pr-stale-when-updated: true