Add validations that respect new allow_mfa_for_subgroups setting

Add specs for new validation

Add validation in group

Add specs for new requires_two_factor_validation

WIP

Update validations for namespace setting

spec/factories/groups.rb

@@ -7,6 +7,7 @@ FactoryBot.define do
     type { 'Group' }
     owner { nil }
     project_creation_level { ::Gitlab::Access::MAINTAINER_PROJECT_ACCESS }
+    association :namespace_settings, factory: :namespace_settings
 
     after(:create) do |group|
       if group.owner
@@ -23,7 +24,7 @@ FactoryBot.define do
     end
 
     trait :internal do
-      visibility_level {Gitlab::VisibilityLevel::INTERNAL }
+      visibility_level { Gitlab::VisibilityLevel::INTERNAL }
     end
 
     trait :private do