Document and test var.grant_registry_access supports artifact registry

[stanley98yu]

Mainly documentation changes, but I added a small change to a test to see if the role is properly assigned. Let me know if I should add anything else.

Issue reference: #1015

[comment-bot-dev]

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[sreenivas-ps]

@stanley98yu : does this enable_confidential_nodes work? I'm using this version "terraform-google-modules/kubernetes-engine/google//modules/beta-private-cluster" but getting this error:

Error: Unsupported argument

  on gke.tf line 70, in module "gke2":
  70:   enable_confidential_nodes = true

An argument named "enable_confidential_nodes" is not expected here.

[stanley98yu]

Hello @sreenivas-ps, I believe the enable_confidential_nodes field should work--see simple_regional_private_beta for an example. My first thought based on what you posted is to try changing the module name to "gke". If the problem persists, please open an issue to get it debugged.