Automatic merge from submit-queue (batch tested with PRs 47113, 46665, 47189)

kube-apiserver: cleanup node proxy setup code

Follow-up of https://github.com/kubernetes/kubernetes/pull/46680, fixing #46679

- move `proxyTransport` from `New` func to config
- use self-explaining variable names
- remove redundant temporary var
- make `CreateNodeDialer` side-effect-free
- make imports follow conventions
- lower-case error messages