GitHub import should respect group limits when importing projects

What does this MR do and why?

GitHub import should respect group limits when importing projects

Changelog: changed EE: true

References

https://gitlab.com/gitlab-org/gitlab/-/issues/559224

How to set up and validate locally

1. Create a project on GitHub.
2. Create a group on GitLab.
3. Import the project from GitHub.
4. Go through the user mapping flow to assign contributions to a member.
5. The imported project should have two direct members:
   • You.
   • The user you mapped the GitHub contributions to.
6. Go to the group settings (/groups/membership-demo-dest/-/edit#js-permissions-settings) and enable "Users cannot be added to projects in this group".
7. Import the project again.
8. The new project should have no direct memberships, only your inherited membership from the parent group.

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