Make nesting depth configurable

[123BLiN]

I'm just testing the waters here, but here is our problem:
we have a lot of protoc definitions for our grpc and they do not have defaults, the resulted generated cli works but people complains that it is hard to use due to the amount of knobs and toggles produced.

One of the possible options could be to allow some fields to be provided as json instead of a set of flags (10-20 of them)
and maybe it can be controlled by some option like nesting_depth so everything that is lower is just wrapped to the single parent parameter?