Support out-of-cluster configuration

[lucaspalm]

Right now, Portieris is installed directly inside the kubernetes cluster in which it manages. It would be great if Portieris had the option to run outside of the cluster as well.

Example out-of-cluster go-client configuration can be seen here.

As long as Portieris is fed the correct cluster Kubeconfig, it should be able to perform the same actions as it does today from within the cluster. The MutatingWebhookConfiguration ClientConfig could then be changed to point directly to the URL of the out-of-cluster Portieris instance. Docs on how that is done are here.

All other kube resources like webhooks, roles, policies, etc. would still be created in the kube cluster as normal.