Feature: pizza generate config flow with existing config

[zeucapua]

Suggested solution

When the user already has a .sauced.yaml configuration file, the pizza generate config command should warn the user that it exists and give them the option of either regenerating/replacing it or use the existing users when attributing new emails.

Context

Having an existing .sauced.yaml, it regenerated it, but the missing premable in comments got removed. Not sure if that's from our template, but just mentioning it.

When regenerating the .sauced.yaml, if one is detected (non-interactive mode) potentially mention it before they proceed.

Also, not sure how far back we're looking by default in the git history, but I see Anush, one of our interns in the list.

Also, we should skip known bot accounts, i.e. any account ending in [bot].

Originally posted by @nickytonline in #137 (review)