Enable frozen string in app/controllers/**/*.rb

Enables frozen string for the following:

* app/controllers/*.rb
* app/controllers/admin/**/*.rb
* app/controllers/boards/**/*.rb
* app/controllers/ci/**/*.rb
* app/controllers/concerns/**/*.rb

Partially addresses #47424.

app/controllers/abuse_reports_controller.rb

+# frozen_string_literal: true
+
 class AbuseReportsController < ApplicationController
   before_action :set_user, only: [:new]

app/controllers/admin/abuse_reports_controller.rb

+# frozen_string_literal: true
+
 class Admin::AbuseReportsController < Admin::ApplicationController
   # rubocop: disable CodeReuse/ActiveRecord
   def index

app/controllers/admin/appearances_controller.rb

+# frozen_string_literal: true
+
 class Admin::AppearancesController < Admin::ApplicationController
   before_action :set_appearance, except: :create

app/controllers/admin/application_controller.rb

+# frozen_string_literal: true
+
 # Provides a base class for Admin controllers to subclass
 #
 # Automatically sets the layout and ensures an administrator is logged in

app/controllers/admin/application_settings_controller.rb

+# frozen_string_literal: true
+
 class Admin::ApplicationSettingsController < Admin::ApplicationController
   before_action :set_application_setting

app/controllers/admin/applications_controller.rb

+# frozen_string_literal: true
+
 class Admin::ApplicationsController < Admin::ApplicationController
   include OauthApplications

app/controllers/admin/background_jobs_controller.rb

+# frozen_string_literal: true
+
 class Admin::BackgroundJobsController < Admin::ApplicationController
   def show
     ps_output, _ = Gitlab::Popen.popen(%W(ps ww -U #{Gitlab.config.gitlab.user} -o pid,pcpu,pmem,stat,start,command))

app/controllers/admin/broadcast_messages_controller.rb

+# frozen_string_literal: true
+
 class Admin::BroadcastMessagesController < Admin::ApplicationController
   include BroadcastMessagesHelper

app/controllers/admin/dashboard_controller.rb

+# frozen_string_literal: true
+
 class Admin::DashboardController < Admin::ApplicationController
   include CountHelper

app/controllers/admin/deploy_keys_controller.rb

+# frozen_string_literal: true
+
 class Admin::DeployKeysController < Admin::ApplicationController
   before_action :deploy_keys, only: [:index]
   before_action :deploy_key, only: [:destroy, :edit, :update]

app/controllers/admin/gitaly_servers_controller.rb

+# frozen_string_literal: true
+
 class Admin::GitalyServersController < Admin::ApplicationController
   def index
     @gitaly_servers = Gitaly::Server.all

app/controllers/admin/groups_controller.rb

+# frozen_string_literal: true
+
 class Admin::GroupsController < Admin::ApplicationController
   include MembersPresentation

app/controllers/admin/health_check_controller.rb

+# frozen_string_literal: true
+
 class Admin::HealthCheckController < Admin::ApplicationController
   def show
     @errors = HealthCheck::Utils.process_checks(['standard'])

app/controllers/admin/hook_logs_controller.rb

+# frozen_string_literal: true
+
 class Admin::HookLogsController < Admin::ApplicationController
   include HooksExecution

app/controllers/admin/hooks_controller.rb

+# frozen_string_literal: true
+
 class Admin::HooksController < Admin::ApplicationController
   include HooksExecution

app/controllers/admin/identities_controller.rb

+# frozen_string_literal: true
+
 class Admin::IdentitiesController < Admin::ApplicationController
   before_action :user
   before_action :identity, except: [:index, :new, :create]

app/controllers/admin/impersonation_tokens_controller.rb

+# frozen_string_literal: true
+
 class Admin::ImpersonationTokensController < Admin::ApplicationController
   before_action :user

app/controllers/admin/impersonations_controller.rb

+# frozen_string_literal: true
+
 class Admin::ImpersonationsController < Admin::ApplicationController
   skip_before_action :authenticate_admin!
   before_action :authenticate_impersonator!

app/controllers/admin/jobs_controller.rb

+# frozen_string_literal: true
+
 class Admin::JobsController < Admin::ApplicationController
   # rubocop: disable CodeReuse/ActiveRecord
   def index

app/controllers/admin/keys_controller.rb

+# frozen_string_literal: true
+
 class Admin::KeysController < Admin::ApplicationController
   before_action :user, only: [:show, :destroy]