Automatic merge from submit-queue (batch tested with PRs 50289, 52106)

Honor --use-service-account-credentials in cloud-controller-manager

If --use-service-account-credentials is specified, the cloud controller manager should honor it

The distinction between the rootclientbuilder and the clientbuilder came from kube-controller-manager, which is responsible for running the very controllers that enable service accounts. That two-layer approach is not needed in the cloud-controller-manager.

```release-note
The `kube-cloud-controller-manager` flag `--service-account-private-key-file` was non-functional and is now deprecated.
The `kube-cloud-controller-manager` flag `--use-service-account-credentials` is now honored consistently, regardless of whether `--service-account-private-key-file` was specified.
```