Feature: option to rebind submission key in interactive mode

[cmpadden]

I think that it would be great to be able to change the key binding of the "submit" key (default: <Enter>) when working with chatblade in interactive mode. I would like to be able to use <Shift-Enter> or something comparable.

Implementation question(s):

• Would you prefer that this be exposed as a command-line argument? Alternatively, if it were to be an option in ~/.config/chatblade, how would we differentiate that from saved prompts?
• Would we still be able to use the rich Prompt.ask method for querying user input? Upon first glance I don't see a way to override key bindings.