github/workflows: introduce release action

Using staging branch for now, due to the new
release_artifacts.

.github/workflows/release.yml

@@ -0,0 +1,16 @@
+name: "Create GitHub release"
+
+on:
+  push:
+    tags:
+      - "v*"
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Upstream release
+        uses: osbuild/release-action@staging
+        with:
+          token: "${{ secrets.SCHUTZBOT_GITHUB_ACCESS_TOKEN }}"
+          slack_webhook_url: "${{ secrets.SLACK_WEBHOOK_URL }}"