chore: Port logout to be pure Rust (#3302)
With this PR `turbo logout` can run without jumping to Go.
Notes:
- Used `config-rs` for our config reading. It doesn't support writing
configs to disk out of the box, but this can be solved with a wrapper
struct. This can probably be abstracted to be generic over different
configs, but we should hold off until that seems beneficial.
- `termcolor` is used for coloring output, this is the same crate that
`env_logger` uses for coloring outputs. The `UI` struct is expected to
be passed into any subcommands that need pretty output.
- A slight behavior change is that we no longer delete the entire config
file and instead make the token null (`"token": null`). If this is
unwanted, I can change it back to the old behavior, but I wanted to test
out `UserConfig::set_token` before someone else tried using it.
Co-authored-by: Leah <github.leah@hrmny.sh>
