GKE Hub enhancements

[bharathkkb]

Currently we support GKE hub membership registration via SA key. Moving forward we should also consider supporting hub memberships via Workload Identity and via kubeconfig for non GCP Kubernetes clusters.

• using Workload Identity

module "hub" {
  source                = "terraform-google-modules/kubernetes-engine/google//modules/hub"
  project_id            = "my-project-id"
  cluster_name          = "my-cluster-name"
  location              = module.gke.location
  cluster_endpoint      = module.gke.endpoint
+ use_workload_identity = true
}

• via kubeconfig
  • kubeconfig will be generated dynamically to prevent diff issues

module "hub" {
  source                = "terraform-google-modules/kubernetes-engine/google//modules/hub"
  project_id            = "my-project-id"
  cluster_name          = "my-cluster-name"
  location              = module.gke.location
  cluster_endpoint      = module.gke.endpoint
+ use_kubeconfig = true
}

TODO:

• [x] #605

[abhinavrau]

@bharathkkb Following up on kubeconfig support, it looks like there is no explicit integration test for the hub module. It is being tested with asm in simple_zonal_with_asm.

To test the use_kubeconfig feature, would it make sense to create a new integration test based on the simple_zonal_with_asm test and use kubeconfig to register with hub?