chore: add enumeration data type to .repo-metadata.json (#197)

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

java-functions/.repo-metadata.json

@@ -1,15 +0,0 @@
-{
-  "name": "functions",
-  "name_pretty": "Cloud Functions",
-  "product_documentation": "https://cloud.google.com/functions",
-  "api_description": "is a scalable pay as you go Functions-as-a-Service (FaaS) to run your code with zero server management.",
-  "client_documentation": "https://googleapis.dev/java/google-cloud-functions/latest/index.html",
-  "release_level": "ga",
-  "transport": "grpc",
-  "language": "java",
-  "repo": "googleapis/java-functions",
-  "repo_short": "java-functions",
-  "distribution_name": "com.google.cloud:google-cloud-functions",
-  "api_id": "cloudfunctions.googleapis.com",
-  "requires_billing": true
-}