List multiple clusters on ClustersController#index

Also:
* Stub out index view
* Adds the clusters before_action that returns all clusters

app/controllers/projects/clusters_controller.rb

 class Projects::ClustersController < Projects::ApplicationController
   before_action :cluster, except: [:login, :index, :new, :new_gcp, :create]
+  before_action :clusters, only: [:index]
   before_action :authorize_read_cluster!
   before_action :authorize_create_cluster!, only: [:new, :new_gcp, :create]
   before_action :authorize_google_api, only: [:new_gcp, :create]
@@ -7,11 +8,6 @@ class Projects::ClustersController < Projects::ApplicationController
   before_action :authorize_admin_cluster!, only: [:destroy]
 
   def index
-    if project.cluster
-      redirect_to project_cluster_path(project, project.cluster)
-    else
-      redirect_to new_project_cluster_path(project)
-    end
   end
 
   def login
@@ -91,6 +87,10 @@ class Projects::ClustersController < Projects::ApplicationController
     @cluster ||= project.clusters.find_by(id: params[:id])&.present(current_user: current_user) || render_404
   end
 
+  def clusters
+    @clusters ||= project.clusters.map { |cluster| cluster.present(current_user: current_user) }
+  end
+
   def create_params
     params.require(:cluster).permit(
       :enabled,

app/views/projects/clusters/index.html.haml

+Hello World!