Add formatting configuration and enable auto-formatting for TOML

[matej-almasi]

Hello, I suggest adding a formatter setting for TOML files to helix's shipped language config and setting auto-format to true.

Reason: Rust has auto format set and working out of the box. TOML is a companion language (of sorts) to Rust, and having auto-formatting for it work by default would align with the batteries included philosophy of Helix.