➕ Add fastapi-new as a dependency

[savannahostrowski]

This PR adds https://github.com/fastapi/fastapi-new as a dependency.

In short, the user journeys are:

• Install fastapi-cli[standard,new] to get all standard FastAPI CLI commands and new ➕ Add fastapi-new in new optional dependency group fastapi/fastapi-cli#241
• Install fastapi-cloud-cli to get cloud commands and new (that's this PR)
• Install fastapi-new to just get the new command.

[tiangolo]

Ah, let's not add it here, let's keep it only as an optional for fastapi-cli.

If we add it here as a default dependency, then installing "fastapi[standard]" will include this, and we don't want it installed by default.

If we installed it by default, people would have both commands fastapi and fastapi-new available, and they would have to manually pick one when triggering shell tab completion, making each command one extra step away (e.g. fastapi dev, fastapi login, fastapi deploy).