Remove master_auth fields from google_container_cluster resource

[upodroid]

Upstream Kubernetes has deprecated and removed basic auth from kubernetes as of v1.19 . In the next major release of the provider, master_auth nested fields needs to be removed given that there are many breaking changes issues open against this resource.

https://cloud.google.com/kubernetes-engine/docs/how-to/api-server-authentication#legacy-auth
rancher/rancher#28673

[rileykarson]

Note: This should only be removed if the lowest available GKE version has removed support for basic auth.

[melinath]

At this point our tests for this feature are consistently failing with:

Basic authentication was removed for GKE cluster versions >= 1.19. The cluster cannot be created with basic authentication enabled. Instructions for choosing an alternative authentication method can be found at: https://cloud.google.com/kubernetes-engine/docs/how-to/api-server-authentication.

Previously they were failing with:

Clusters with minor version 1.18 and basic authentication enabled cannot migrate to rapid, regular or stable release channels. Basic authentication was removed for GKE cluster versions >= 1.19. To disable basic authentication use: gcloud container clusters update %s --no-enable-basic-auth. Instructions for choosing a new method can be found at: https://cloud.google.com/kubernetes-engine/docs/how-to/api-server-authentication.

It's not exactly clear to me whether existing clusters might still be running 1.18, but it seems likely that creating new clusters now requires not using basic auth.

[rileykarson]

1.18.0, 1.19.0, and 1.20.0 are the currently supported GKE versions: https://cloud.google.com/kubernetes-engine/docs/release-notes

So we're one more version away from being able to do this.

[github-actions]

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