Cluster discovery

[Fryguy]

This enhancement is more for the subclasses of the kubernetes provider, particularly for the ones that are part of a Cloud provider, such as EKS and IKS. In those environments we already have the user's credentials for the Cloud side of things, and could automate adding Kubernetes clusters directly from those credentials.

I can picture it as a "Discover Kubernetes Clusters" option as part of the authentication screen, but would love some input on how better to design this. There might be a bigger picture design here for discovery on other platforms as well.

This might dovetail a little bit with #509 where adding the cluster could also add a service account at the same time.