chore: update .repo-metadata.json (#260)

Author: parthea

.repo-metadata.json

@@ -4,13 +4,14 @@
     "product_documentation": "https://cloud.google.com/bigquery/transfer/",
     "client_documentation": "https://cloud.google.com/python/docs/reference/bigquerydatatransfer/latest",
     "issue_tracker": "https://issuetracker.google.com/savedsearches/559654",
-    "release_level": "ga",
+    "release_level": "stable",
     "language": "python",
     "library_type": "GAPIC_AUTO",
     "repo": "googleapis/python-bigquery-datatransfer",
     "distribution_name": "google-cloud-bigquery-datatransfer",
     "api_id": "bigquerydatatransfer.googleapis.com",
     "requires_billing": true,
     "default_version": "v1",
-    "codeowner_team": "@googleapis/api-bigquery"
+    "codeowner_team": "@googleapis/api-bigquery",
+    "api_shortname": "bigquerydatatransfer"
 }