…to stop copy pasting test cases.

Fix LDAP config key name

See merge request gitlab-org/gitlab-ce!14739

Create idea of read-only database

Closes #37534

See merge request gitlab-org/gitlab-ce!14688

Create merge requests across a fork network

Closes #20097

See merge request gitlab-org/gitlab-ce!14422

So we can keep showing it to a user in his project page.

This uses the existing ForkedProjectLinks

The helper creates a fork of a project with all provided attributes,
but skipping the creation of the repository on disk.