Support for a global config file

[rafaScalet]

Is your feature request related to a problem? Please describe.

Describe the solution you'd like

Add support for a global config file as a fallback if one in the current directory didn't exist, and if a global config file didn't exist too, return an error.

Describe alternatives you've considered

a config file in: $HOME/.config/treefmt/config.toml or $HOME/.config/treefmt.toml to respect the XDG spec

Additional context

[jfly]

I am not supportive of this, as I would prefer people strive to keep their individual repos "self contained". See #619 for a related discussion.

[brianmcgee]

Having a fallback global config file implies a default global set of formatters that must be available in your PATH.

Since I typically use treefmt within nix devshells, this approach feels very foreign. That being said, I'm open to understanding if this is valuable.

@rafaScalet, what would a typical use case for this be? Put another way, if this were implemented, what would your default global formatters/config be?

[rafaScalet]

My idea with this feature would be integration with other tools, such as IDEs. I use Neovim, and I use a plugin called conform.nvim, which allows me to configure formatters for each language. With global configuration support, I could remove this plugin and use simple Neovim APIs to integrate with Treefmt (simpler, without abstractions, everything under my control).

I know I can integrate Neovim without global configuration support, but it would be much easier if I had it, so I wouldn't need to create a file for each project.