Add frozen_string_literal to new files

app/controllers/groups/clusters/applications_controller.rb

+# frozen_string_literal: true
+
 class Groups::Clusters::ApplicationsController < Groups::ApplicationController
   before_action :cluster
   before_action :application_class, only: [:create]

spec/controllers/groups/clusters/applications_controller_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 describe Groups::Clusters::ApplicationsController do