Groups API: Add Restrict group access by Domain

Proposal

Currently the only way to add domain restrictions at the group level is via the UI. Requesting that API capability be added to the Groups API in order to restrict access to groups by domain programmatically.

Availability and Testing

No new E2E updates or tests needed at this time. Please ensure coverage in unit and integration tests, and consider adding a new API request spec.

Documentation

• https://docs.gitlab.com/ee/user/group/access_and_permissions.html#restrict-group-access-by-domain
• https://docs.gitlab.com/ee/api/groups.html#update-group