Add workflow for cleaning up previews on schedule

Author: giordano

.github/workflows/DocPreviewsCleanup.yml

@@ -0,0 +1,32 @@
+name: Doc Previews Cleanup
+
+on:
+  schedule:
+    - cron: "25 22 * * 2"
+  workflow_dispatch:
+
+concurrency:
+  # Same group concurrency as the `Documentation.yml` workflow, because they both
+  # git-push to the same branch, so we want to avoid clashes.
+  group: docs-pushing
+
+jobs:
+  doc-preview-cleanup:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Checkout gh-pages branch
+        uses: actions/checkout@v6
+        with:
+          ref: gh-pages
+      - name: Delete preview and history + push changes
+        run: |
+          if [[ -d previews ]]; then
+            git config user.name "${{github.actor}}"
+            git config user.email "${{github.actor_id}}+${{github.actor}}@users.noreply.github.com"
+            git rm -rf previews/
+            git commit -m 'Delete previews directory'
+            git branch gh-pages-new $(echo "Delete history" | git commit-tree HEAD^{tree})
+            git push --force-with-lease origin gh-pages-new:gh-pages
+          fi