Use the user list from the target project in a merge request
What does this MR do?
This MR derives the assignable users from the target project.
Why was this MR needed?
In a merge request, the assignable users uses the list from the forked project, not the target project where the merge request will be going. For example, if I fork a project from the gitlab-org namespace into my personal namespace, make some changes, and then create a merge request, the only users I see are me. I think it makes more sense to show all the users in gitlab-org. This is a regression caused by 1c2711f7.
What are the relevant issue numbers?
Closes #1535 (closed)