feat: interactive project initialisation

[Procrat]

Counterpart of shuttle-hq/shuttle#498

[oddgrd]

Hey Procrat, good thinking on updating the docs! I am wondering though, if we remove the project new step from the examples but keep the init call as is (cargo shuttle init --axum) the project (the deployer container) won't have been created before the deploy step. Perhaps we should just keep the project new step?

Alternatively we could change to just init and tell the user to choose a unique name and the correct framework. For the quickstart page we should probably do that, but tell the user to choose the framework they want.

[Procrat]

Like I implemented it (but let me know if it's not ideal), cargo shuttle init --axum will still start an interactive mode that'll ask whether the user wants to create an environment. It's only when both the framework and the project name are supplied that it won't prompt for anything. Should I change it everywhere to that perhaps?

[oddgrd]

Oh, right! I only tested this with the name arg included (and I doubt the user will do that). I think it's perfect like this then, thanks!