chore: add enumeration data type to .repo-metadata.json (#806)

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

.repo-metadata.json

@@ -1,17 +1,18 @@
 {
-  "name": "bigquerydatatransfer",
-  "name_pretty": "BigQuery Data Transfer Service",
-  "product_documentation": "https://cloud.google.com/bigquery/transfer/",
-  "client_documentation": "https://googleapis.dev/java/google-cloud-bigquerydatatransfer/latest",
-  "api_description": "transfers data from partner SaaS applications to Google BigQuery on a scheduled, managed basis.",
-  "issue_tracker": "https://issuetracker.google.com/savedsearches/559654",
-  "release_level": "ga",
-  "language": "java",
-  "repo": "googleapis/java-bigquerydatatransfer",
-  "repo_short": "java-bigquerydatatransfer",
-  "distribution_name": "com.google.cloud:google-cloud-bigquerydatatransfer",
-  "codeowner_team": "@googleapis/api-bigquery",
-  "api_id": "bigquerydatatransfer.googleapis.com",
-  "transport": "grpc",
-  "requires_billing": true
-}
+    "name": "bigquerydatatransfer",
+    "name_pretty": "BigQuery Data Transfer Service",
+    "product_documentation": "https://cloud.google.com/bigquery/transfer/",
+    "client_documentation": "https://googleapis.dev/java/google-cloud-bigquerydatatransfer/latest",
+    "api_description": "transfers data from partner SaaS applications to Google BigQuery on a scheduled, managed basis.",
+    "issue_tracker": "https://issuetracker.google.com/savedsearches/559654",
+    "release_level": "ga",
+    "language": "java",
+    "repo": "googleapis/java-bigquerydatatransfer",
+    "repo_short": "java-bigquerydatatransfer",
+    "distribution_name": "com.google.cloud:google-cloud-bigquerydatatransfer",
+    "codeowner_team": "@googleapis/api-bigquery",
+    "api_id": "bigquerydatatransfer.googleapis.com",
+    "transport": "grpc",
+    "requires_billing": true,
+    "library_type": "GAPIC_AUTO"
+}