Use context when switching to kind-porter

[troy0820]

• Add kubectl config use-context kind-porter when executing script (mage Deploy needs this)
• Combine kubeconfig with existing kubeconfig env var.

No test needed.

[troy0820]

Checking to see if this works with some go.work magic.

[troy0820]

CreateCluster exports the CreateTestCluster to test this. This mage target is not committed.

[schristoff]

I wonder what happens if we run this twice, does it just error out if there's an existing kind-porter cluster? Anyways, lgtm :) maybe a thing we should make an issue for and deal with later tho