Remove kubernetes dashboard addon

[Shashindran]

The Kubernetes Dashboard addon is removed for clusters on GKE.

This causing this error:

Error: "addons_config.0.kubernetes_dashboard": [REMOVED] The Kubernetes Dashboard addon is removed for clusters on GKE.

  on .terraform/modules/gke/terraform-google-modules-terraform-google-kubernetes-engine-ab02f24/modules/private-cluster/cluster.tf line 22, in resource "google_container_cluster" "primary":
  22: resource "google_container_cluster" "primary" {

Fixed by removing the dashboard addon config in cluster.tf and updated main.tf and output.tf.

[morgante]

Thanks for working on this! Looks like you also need to regenerate docs (with make generate_docs) to get the linters passing (you can check locally with make docker_test_lint).