Local configuration folder

[jdrouet]

Hi everyone!
First, thank you for that amazing work!

Describe your feature request

I'm working on a big codebase that takes several minutes to build. So I've to disable features in order to make it run faster.
I can do that by passing arguments to rust-analyzer in the languages.toml config file.
The problem is that it applies for every helix instances.

I'd love to have a .helix folder in the project folder with a languages.toml file in it to disable features only for the current project.

[hemedani]

also, it's good for disabling the typescript language server and enabling deno lsp on deno project.

please document this feature for deno and typescript.