Add two new constructors for versioned and unversioned RESTClients.
These new constructors allow to pass an http.Client to the RESTClient,
taking precence over the transport Config parameters.
Add a new helper function to generate an http.Client from the RESTClient
Config object.
Co-authored-by: Jordan Liggitt <liggitt@google.com>
Kubernetes-commit: 80fbc817263de1c46e1493819aca35b1ef8e3d09