Default to :all scope for ClustersController#index

app/controllers/projects/clusters_controller.rb

@@ -7,7 +7,7 @@ class Projects::ClustersController < Projects::ApplicationController
   before_action :authorize_admin_cluster!, only: [:destroy]
 
   def index
-    @scope = params[:scope]
+    @scope = params[:scope] || :all
     clusters = ClustersFinder.new(project, current_user, @scope).execute
     @clusters = clusters.page(params[:page]).per(20)
     @active_count = project.clusters.enabled.count