Create Settings::BaseController (#9507)

Define `Settings::BaseController#set_body_classes` so that sub classes
inherit `Settings::BaseController` don't need to define
`#set_body_classes` agein.

app/controllers/settings/two_factor_authentications_controller.rb

@@ -1,12 +1,11 @@
 # frozen_string_literal: true
 
 module Settings
-  class TwoFactorAuthenticationsController < ApplicationController
+  class TwoFactorAuthenticationsController < BaseController
     layout 'admin'
 
     before_action :authenticate_user!
     before_action :verify_otp_required, only: [:create]
-    before_action :set_body_classes
 
     def show
       @confirmation = Form::TwoFactorConfirmation.new
@@ -44,9 +43,5 @@ module Settings
       current_user.validate_and_consume_otp!(confirmation_params[:code]) ||
         current_user.invalidate_otp_backup_code!(confirmation_params[:code])
     end
-
-    def set_body_classes
-      @body_classes = 'admin'
-    end
   end
 end