chore: update release-level in .repo-metadata.json (googleapis#700)

Author: Neenu1995

java-resourcemanager/.repo-metadata.json

@@ -4,7 +4,7 @@
   "product_documentation": "https://cloud.google.com/resource-manager",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-cloud-resourcemanager/latest/history",
   "issue_tracker": "https://issuetracker.google.com/savedsearches/559757",
-  "release_level": "ga",
+  "release_level": "stable",
   "language": "java",
   "repo": "googleapis/java-resourcemanager",
   "repo_short": "java-resourcemanager",