Use mergify to merge PRs for stream to lake sync

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sutaakar

.github/workflows/auto-merge-lake-gate.yml

@@ -0,0 +1,12 @@
+pull_request_rules:
+  - name: Auto-merge lake-gate PRs to stable
+    conditions:
+      - base=stable
+      - label=lake-gate
+      - -draft
+      - -closed
+      - author=github-actions[bot]
+      - check-success~=^Red Hat Konflux.*
+    actions:
+      merge:
+        method: fast-forward