Interactive config creator

[GideonBear]

I want to suggest some general feature

Ability to generate an initial config file via topgrade --init-config (or in the first run) prompting the user with choices on what they want to include in the config file (unlike the --config-reference flag which just outputs a hardcoded example file).

(Original request in #359 by @phanirithvij)

[GideonBear]

Comments from #359:

I did not used the command yet, but the config file is a monster to approach, and one may want to understand how an executor is found and its options before starting a command this important on their own system.

@Zykino