Something I've been wanting for a long time, but have been put up because of how it's going to be done.

Raising it again now, because once there's some agreement on delineation in #642, we ought to do this to fix dependabot issues (users get dependabot issues for kube and kube_runtime separately, which is incompatible with our versioning policy).

• Failed attempt: through exposing Api as an async trait: see Make an async_trait for Api trait to remove kube dependency from kube-runtime #592
• Likely route: pull api and config modules into one or two new crates
• Import new crate(s) from kube
• Can now re-export kube-runtime from kube under a runtime feature

=> kube is a facade crate only the only thing users depend on