FR: jj setup command to prompt user for name/email/settings

[Cretezy]

Is your feature request related to a problem? Please describe.
When setting up jj, everyone must run jj config set --user user.name ... && jj config set --user user.email ....

Describe the solution you'd like
A command such as jj setup which asks the user for their name, email, and other relevant settings. This command can use the current values set in the config, as well as read from .gitconfig for name/email to simplify setup.

This could use https://github.com/mikaelmello/inquire

Example flow:

$ jj setup
? What is your name: 
? What is your email:

I can make a PR if this is approved.

[PhilipMetzger]

I don't think that a command is necessary for that, although it probably should land in jj init when we have multiple backends see #2747 (comment).