Add ability to generate v3.Cluster

[richardcase]

Add an alternative import strategy to Rancher Turtles that will generate a management.v3.Cluster instead of a provisioning.v1.Cluster.

This is to ensure that we can support this scenario in light of future changes to Rancher.

A small amount of investigation was done: rancher/highlander#42

[richardcase]

I suggest that we add a new feature flag that when set to true will enable a slightly different import strategy.

The alternative strategy will:

• Generate a management.cattle.io/v3/Cluster with DisplayName in the spec (and also probably Description). We'll need to use generateName for example:

apiVersion: management.cattle.io/v3
kind: Cluster
metadata:
  generateName: c-
spec:
  displayName: "child1"
  description: "some cluster created by capi"

• If Connected status is true then we could probably exit early
• Get the ClusterRegistrationToken from the namespace with the same name as the v3.Cluster
• Apply the import manifests to the schild cluster (like we do now)