Artman code generation: can't configure channel size

[kmjung]

I use artman to generate Java client libraries for my gRPC-based service. Specifically, I'm using the googleapis and toolkit versions from this commit: googleapis/artman@d065fbb

My service interface requires that I increase the inbound message size up to 10 mb. However, it doesn't appear that this option is supported currently in artman / gapic -- I had to manually edit the emitted code to make this work.

[kmjung]

Coped to http://github.com/googleapis/toolkit: googleapis/gapic-generator#1732