chore: update repo-metadata file

Author: Neenu1995

.repo-metadata.json

@@ -4,7 +4,7 @@
   "product_documentation": "https://cloud.google.com/solutions/retail",
   "api_description": "Retail solutions API.",
   "client_documentation": "https://googleapis.dev/java/google-cloud-retail/latest/index.html",
-  "release_level": "beta",
+  "release_level": "ga",
   "transport": "grpc",
   "language": "java",
   "repo": "googleapis/java-retail",