Make it possible to take the input as an interactive prompt

Looks good, thanks. Do we need to update the docs for this? Seems intuitive enough to not really need mentioning 🤷

The other thing I'd like to have when entering drush ai is an interactive shell that continuously chats with you back and forth.

Thanks @ marcus_johansson → and @ robloach → ! The current implementation is intuitive and doesn’t require additional documentation. As noted, it would be great to explore the possibility of having an interactive shell mode for drush ai in future iterations — where it maintains a continuous back-and-forth chat experience.

I made a slight change in the order, so the interactive prompt doesn't show up if no default or set provider is set. Please rereview.