Remove support for Kubernetes basic auth

[Ebaneck]

Component:

'kubernetes', 'salt'

Why this is needed:

With the introduction of OIDC(a new way to Adding or removing users) in MetalK8s there is no longer the need to continue to support the basic file-based authentication system and hence needs to be removed.

What should be done:

• Remove the htpasswd file from the Kubernetes apiserver manifest
• Remove htpasswd from the salt tree

Implementation proposal (strongly recommended):

Test plan:

Test & verify that authentication in MetalK8s still works with OIDC flow