Support user defined kubeconfig, fix merging context

[dereknola]

Signed-off-by: Derek Nola [email protected]

Changes

This is a follow on to discussion in #263

• Adds new var kubeconfig which if specified copies the ansible cluster kubeconfig to that path location
• Cleans up merging of kuebconfig context under default conditions. Now covers the cases of:
  • Kubectl is not installed on the control node
  • An existing cluster is already using the default context. We now merge everything under the k3s-ansible context/cluster/user.
  • Swapping to a different inventory.yml setup and deploying again. We correctly overwrite the k3s-ansible context.