Update MemberRoles::RolesFinder as part of instance-level custom roles migration
Right now, on self-managed, we have both instance-level and grou-level custom roles. In %17.0 we are migrating self-managed customers to use only instance-level custom roles.
As part of this migration we should make sure whenever we retrieve custom roles for self-managed, we retrieve instance-level custom roles while for SaaS, we should always filter by group