chore: add enumeration data type to .repo-metadata.json (#170)

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

.repo-metadata.json

@@ -1,15 +1,16 @@
 {
-  "name": "security-private-ca",
-  "name_pretty": "Certificate Authority Service",
-  "product_documentation": "https://cloud.google.com/certificate-authority-service/docs",
-  "api_description": "simplifies the deployment and management of private CAs without managing infrastructure.",
-  "client_documentation": "https://googleapis.dev/java/google-cloud-security-private-ca/latest/index.html",
-  "release_level": "beta",
-  "transport": "grpc",
-  "language": "java",
-  "repo": "googleapis/java-security-private-ca",
-  "repo_short": "java-security-private-ca",
-  "distribution_name": "com.google.cloud:google-cloud-security-private-ca",
-  "api_id": "security-privateca.googleapis.com",
-  "requires_billing": true
-}
+    "name": "security-private-ca",
+    "name_pretty": "Certificate Authority Service",
+    "product_documentation": "https://cloud.google.com/certificate-authority-service/docs",
+    "api_description": "simplifies the deployment and management of private CAs without managing infrastructure.",
+    "client_documentation": "https://googleapis.dev/java/google-cloud-security-private-ca/latest/index.html",
+    "release_level": "beta",
+    "transport": "grpc",
+    "language": "java",
+    "repo": "googleapis/java-security-private-ca",
+    "repo_short": "java-security-private-ca",
+    "distribution_name": "com.google.cloud:google-cloud-security-private-ca",
+    "api_id": "security-privateca.googleapis.com",
+    "requires_billing": true,
+    "library_type": "GAPIC_AUTO"
+}

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-security-private-ca.git",
-        "sha": "3bdb40e5de459353ef51f3a4d2640b355a5842ae"
+        "sha": "07d2611bad70123f68b244d70dcec24a0e8dd331"
       }
     }
   ]