Remove direct dependency on bevy_lint from bevy_cli

[BD103]

This PR makes bevy_lint optional when installing bevy_cli. This solves a number of issue:

• Nightly is technically no longer required for the main CLI, though I'm going to address that in a follow-up.
• If you made a change to the bevy_lint crate, you used to have to run cargo build -p bevy_cli --bin bevy_lint_driver for them to be applied.

In order to do this, I:

• Made bevy lint a facade command that passes all arguments to a bevy_lint binary, if it can be found.
• Added the bevy_lint binary to the bevy_lint crate, and moved bevy_lint_driver to bevy_lint.

Now, nothing lint-related will be installed if bevy_lint isn't except for the facade command.

[janhohenheim]

Looks good, just some minor suggestions :)