Define a custom config path

[pomek]

📝 Provide a description of the new feature

My project defines the mrgit.json content, and I can't modify it, while I really need to add additional entries to my config.

It would be nice to have an option to define a custom mrgit config path when executing mrgit commands, e.g.:

mrgit --config ./my-mrgit.json sync

Instead of looking for the mrgit.json file, the tool tries to load the my-mrgit.json file.

I do not have to commit this file as I can use the global git ignore pattern (https://docs.github.com/en/get-started/git-basics/ignoring-files#configuring-ignored-files-for-all-repositories-on-your-computer).

Definition of Done

• Support for defining a custom config instead of using the default one.
• Update README (include the new option).
• Add the new option to mrgit --help