feat(renovate): enable useBaseBranchConfig for branch-specific configs

renovate.json

@@ -11,6 +11,7 @@
   "labels": [
     "renovate"
   ],
+  "useBaseBranchConfig": "merge",
   "kubernetes": {
     "managerFilePatterns": [
       "/(^|/)kubernetes/.+/[^/]+\\.ya?ml$/"