Support running in & out of Rancher Manager cluster

[richardcase]

Story
As a Rancher Operator,
I want the choice to deploy Rancher Turtles in the same or a different cluster to Rancher Manager,
So that i have choice in my deployment topology.

Description
Currently, its assumed thats the operator is running in the same cluster as Rancher Manager. Change the operator so you can optionally supply a reference to a kubeconfig to use (via a secret) instead of using the incluster credentials.

• [PROPOSAL] Support running in & out of Rancher Manager cluster #186
• Change the operator to optionally support using a kubeconfig for creating a client in addition to the in cluster (Ensure operator can run side-by-side with Rancher #19)
• Define & document RBAC permissions for the kubeconfig (i.e. least privilege)
• e2e test covering both deployment models

[salasberryfin]

As part of rancher/turtles-docs#13, we're doing a collaborative effort to define the workflow for a Rancher operator to be able to use the out of cluster installation topology, including:

• kubeconfig generation.
• least privilege permissions required.
• e2e test scenario.

[salasberryfin]

We're pushing for the in-cluster functionality for Early access - release 1 and will be coming back to this for the next iteration.