Delegate merging of style files to another Python package

[andreoliwa]

Problem

Style files are TOML files that can include other TOML files.

Merged style files are something that Nitpick shouldn't even handle.
This should be separated into another package, but back then I didn't find any Python package that could do the job (I didn't search much, to be honest).

I'd like to get rid of the "merging config files" and delegate it to some other package, if possible.
Maybe even accept formats other than TOML.

This might even fix these related issues: #464, #417

The current style handling is suboptimal, validation is lacking and there are a few loose ends.
Nitpick should only focus on checking/autofixing files which is already a huge task.

Possible solution

• I would like something similar to the extends config on Renovate: Configuration Options - Renovate Docs | Renovate Docs
• I also read the word "merging" in the Dynaconf docs: Merging - Dynaconf - 3.1.7, but I didn't dig deep enough to check if this would work for Nitpick.
• Dynaconf also allow multiple formats like YAML, INI, JSON: Dynaconf - 3.1.7
• Dynaconf allows merging files: Merging - Dynaconf - 3.1.7