feat: kubeconfig path flag

[bbensky]

This PR fixes #

Checklist

• [X] I have signed the CLA
• [X] I have updated/added any relevant documentation

Description

What's the goal of this PR?

Adds the a kubeconfig flag to the nova command, so kubeconfig file paths can be used.

What changes did you make?

Added the kubeconfig flag, and included it as an option when generating the Kubernetes client config.

What alternative solution should we consider, if any?