Clearer notification when unauthenticated

[TrueWill]

Is your feature request related to a problem? Please describe.

I ran k9s when my credentials had expired, and I didn't realize it. Everything behaved oddly (I couldn't change contexts or namespaces, commands like :pod gave "command not found"), but the contexts displayed. I saw no indication that I was not authenticated.

kubectl get nodes displayed

couldn't get current server API group list: the server has asked for the client to provide credentials

which helped me figure it out.

Describe the solution you'd like

Please make it very, very obvious when the user is not authenticated.