Create helper methods for file-level resources 

Proto annotations allows for resources to be described at the file level instead of being a method option.

E.g. 
```proto
// Define a "User" resource owned by OS Login.
option (google.api.resource_definition) = {
  type: "oslogin.googleapis.com/User"
  pattern: "users/{user}"
};
```

These resources also need generated helper methods.