Add option to use `fmt`

[SichangHe]

It would be great to add an option to use fmt for formatting.

To use fmt, user need to have it installed:

raco pkg install fmt

and give it the file to format:

raco fmt -i file_name.rkt

I suggest maybe adding an option that says "command to run for formatting"would do.

[suxiaogang223]

Hi, i love racket and vscode. I wrote this extension before and I wanted to try to add this feature to this extension.👀 https://github.com/suxiaogang223/racket-fmt

[SichangHe]

Go ahead. I am not using Racket on VSCode any more so I won't be testing these. But, you can keep this issue if you want.

[tien]

Would be awesome to have this as an option 🙏