E2E test for Praefect replication

Add an E2E test of basic Praefect replication

It should verify that a push made to a primary node is replicated to a secondary node.

We should also have a test with postgres as the replication database because that's intended to be the default.

Steps

1. Launch a gitlab-qa scenario with Praefect configured with a primary and a secondary node.
2. Create a project and push a file.
3. Verify that the change was pushed successfully.
4. Verify that the change was replicated to the secondary (this might require file system access, e.g., to docker exec into the relevant container)