Custom roles GraphQL: Use SubscriptionHelper for SaaS checks
In !138644 (merged) we introduced the SubscriptionHelper
to check if an instance is on SaaS when running GrahpQL queries. We should use this also for custom roles GraphQL endpoints.
This was brought up in recent merge request - we should replace Gitlab::Saas.feature_available?(:group_custom_roles)
SaaS checks with this. See the thread for more context.
Edited by Jarka Košanová