Refactor project migration specs to run using 2 gitlab instances

What does this MR do and why?

Updates gitlab project migration tests to use orchestrated setup with 2 gitlab instances.

Closes: https://gitlab.com/gitlab-org/gitlab/-/work_items/118773022
Part of: #382166 (closed)

How to set up and validate locally

gitlab-qa Test::Integration::Import EE --qa-image ${qa_image}

MR acceptance checklist

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