Add option to disable namespace validation

[sbstp]

Fixes #59

[sbstp]

@rombert works for you?

[rombert]

Thanks for preparing the changes, @sbstp ! With the PR applied, kubie ctx -n $NS $CTX works, but kubie ctx $CTX followed by kubie ns $NS does not. The error is the same:

User ... cannot list resource "namespaces" in API group "" at the cluster scope

[sbstp]

Thanks for testing, there was indeed an issue with the code. Can you try again?

[rombert]

It works perfectly now, thanks @sbstp !