[FEAT] add the ability to compare two different configurations

[stefanobartoletti]

It would be nice to have a way to compare two different full configurations, and be able to highlight only rules that are different between them.

A possible example would be to compare config-1 and config-2 and only have a list of rules that

• both configs are setting, but with different values
• one of them is setting, while the other is not

basically the same logic behind a common diff in a git context, for example.

This is just a "nice to have" suggestion, nothing really urgent or critical, but maybe it can be considered for addition if time and resources allow for it. It is a feature simple to describe, but I guess that the implementation could be somewhat complex.

Thanks anyway for this package, that is already great in the current state :)

[voxpelli]

I was working on a command line version of that here: https://github.com/voxpelli/compare-eslint-configs

Still planning to update it to ESLint 9 and flat configs: voxpelli/compare-eslint-configs#46