The API isn't using the appropriate services for managing forks
In the API it is possible to mark an existing project as a fork of another project, however, this endpoint does not use a service to do so, it just creates the ForkedProjectLink which means the new ForkNetwork and ForkNetworkMember aren't created:
Further, when unlinking a fork, the API does not use the Projects::UnlinkForkService
This means that some ForkedNetworkMember models might be left when unlinking a fork using the API.
/cc @DouweM @fjsanpedro