Improve make-gen

[leovct]

make gen was designed as a quick way to automatically generate docs, proto, go bindings, go loadtest modes and json rpc types. The aim was to have a deterministic way of generating such files. It is used by the CI to check that the files generated are up to date. It is also used by developers to update these files. Most of the time, they use this command when the CI fails. However the UX is quite bad and there is no documentation on how to use the tool... We should think of 1) improving the documentation and 2) exploring better ways to generate bindings using docker containers - this would avoid the need to install tools locally just to generate a few files.

For reference: https://github.com/0xPolygon/polygon-cli/blob/main/Makefile#L81-L82