Add subcommand for `generate` that outputs a report on what types are supported with code gen

[desaikd]

As we work on a 1.0 for code generation tool, there are few constraints not supported yet. By creating subcommand(e..g check?) within generate to check all the schema files in given authority(s) and return a report on what schema types are not supported for code generation with the reasoning around which constraints are not supported.