Generate --repl and --chat tags automatically

[jeanlucthumm]

One annoying part of sgpt workflow right now is having to come up with conversation tags beforehand. Things like ChatGPT web UI will title the conversations automatically so there's no toil on the user side.

We could auto-gen the tag based on the first prompt. Picturing something like

$ sgpt --auto --chat "Is tomato really a fruit?"
Autotag: fruit_discussion

Yes, a tomato is scientifically classified as a fruit because it develops from the ovary of a flower...