Enable lockFileMaintenance in Renovate config

This ensures Renovate periodically updates lockfile-only dependencies
(transitive deps and those without version pins) that would otherwise
never get updated.

Author: mensfeld

renovate.json

@@ -26,5 +26,8 @@
   "labels": [
     "dependencies"
   ],
-  "minimumReleaseAge": "7 days"
+  "minimumReleaseAge": "7 days",
+  "lockFileMaintenance": {
+    "enabled": true
+  }
 }