T8795: replace inline Mergify config with extends: mergify central baseline

Author: andamasov

.github/mergify.yml

@@ -1,10 +1,3 @@
-pull_request_rules:
-  - name: Label conflicting pull requests
-    description: Add a label to a pull request with conflict to spot it easily
-    conditions:
-      - conflict
-      - '-closed'
-    actions:
-      label:
-        toggle:
-          - conflicts
+extends: mergify
+merge_protections_settings:
+  reporting_method: check-runs