ProtectedBranch API includes user_id/group_id in access levels

What

Includes user_id and group_id as part of ProtectedRefAccess entity

Why

Before this information wasn't included, instead using a human description of the group name or user's full name

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend

Related

Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/35867

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/4152