✨ Improve UI for `fastapi dev` and `fastapi run`

[patrick91]

This PR adds rich-toolkit to improve the look and feel of the app, for now we are only updating the server commands 😊

In terms of the code, I've most of the output out from the discover file into the main cli file (better to keep those utils simpler without any output)

Some potential improvements:

• ~~Better errors~~
• Different colors for different log levels

[patrick91]

There's a small issue when pressing CTRL+C:

you can see ^C (this is sent by the terminal), I have some ideas on how to workaround this, but I don't think it is worth doing it in this PR (if worth doing it at all)