chore: add enumeration data type to .repo-metadata.json (#390)

Adds a standard enumeration of library types in .repo-metadata.json

.repo-metadata.json

@@ -1,16 +1,17 @@
 {
-  "name": "bigqueryconnection",
-  "name_pretty": "Cloud BigQuery Connection",
-  "product_documentation": "https://cloud.google.com/bigquery/docs/reference/bigqueryconnection/rest",
-  "api_description": "allows users to manage BigQuery connections to external data sources.",
-  "client_documentation": "https://cloud.google.com/bigquery/docs/reference/reservations/rpc/google.cloud.bigquery.reservation.v1beta1",
-  "release_level": "ga",
-  "transport": "grpc",
-  "language": "java",
-  "repo": "googleapis/java-bigqueryconnection",
-  "repo_short": "java-bigqueryconnection",
-  "distribution_name": "com.google.cloud:google-cloud-bigqueryconnection",
-  "codeowner_team": "@googleapis/api-bigquery",
-  "api_id": "bigqueryconnection.googleapis.com",
-  "requires_billing": true
-}
+    "name": "bigqueryconnection",
+    "name_pretty": "Cloud BigQuery Connection",
+    "product_documentation": "https://cloud.google.com/bigquery/docs/reference/bigqueryconnection/rest",
+    "api_description": "allows users to manage BigQuery connections to external data sources.",
+    "client_documentation": "https://cloud.google.com/bigquery/docs/reference/reservations/rpc/google.cloud.bigquery.reservation.v1beta1",
+    "release_level": "ga",
+    "transport": "grpc",
+    "language": "java",
+    "repo": "googleapis/java-bigqueryconnection",
+    "repo_short": "java-bigqueryconnection",
+    "distribution_name": "com.google.cloud:google-cloud-bigqueryconnection",
+    "codeowner_team": "@googleapis/api-bigquery",
+    "api_id": "bigqueryconnection.googleapis.com",
+    "requires_billing": true,
+    "library_type": "GAPIC_AUTO"
+}