This was generating fine before but it makes it explicit in the proto
and it avoids weirdness where the protobuf tag will say a name is
something like requestId where the json tag says it's request_id. This
way they line up.
One thing not honoring this properly is TraceId. I don't know why the
JSON tag being generated doesn't match even when explicitly set here.
For now I'm just manually fixing it.
Jeff Mitchell