Ruby: create "v1.rb" pattern into gax template

[jmuk]

This (version).rb is a pattern to simplify the require statement for Ruby.

I've hand-written this for existing APIs like https://github.com/GoogleCloudPlatform/google-cloud-ruby/blob/master/google-cloud-pubsub/lib/google/cloud/pubsub/v1.rb, but packman should generate files like this automatically.

[jmuk]

Cc: @swcloud, @landrito , @geigerj