Expose enterprise_group_id and enterprise_group_associated_at via Users API.
enterprise_group_id
enterprise_group_associated_at
DB entry: https://gitlab.com/gitlab-org/gitlab/-/blob/507355a5175d0ba2c3063875d5b544625649fed3/db/structure.sql#L23609-23610
The purpose is to allow those with admin access to check the user's status.