Move #set_user to Admin::BaseController (#9470)

* Move #set_user to Admin::BaseController

* Rename Admin::TwoFactorAuthenticationsController

from `#set_user` to `#set_target_user` .

app/controllers/admin/base_controller.rb

@@ -15,5 +15,9 @@ module Admin
     def set_body_classes
       @body_classes = 'admin'
     end
+
+    def set_user
+      @user = Account.find(params[:account_id]).user || raise(ActiveRecord::RecordNotFound)
+    end
   end
 end