Enable clap color feature flag

[matteosantama]

Coming from poetry I was struck by how plain rye's help output is. IMO poetry goes a too far with the colors, but a little styling goes a long way to make the output more readable.

clap's color feature flag is a bit of a misnomer -- by default it does not add colors. A lot of thought went into making clap's help output polished, and I think it would be a nice addition to rye.