Draft: CI: Leverage Gitaly setting up seed repos

What does this MR do?

GitLab uses plain Git to setup the testing repository and perform other Git operations. This change leverages Gitaly to do so, and with that move towards Gitaly being able to run as a container on the side more easily. That would require additional changes though.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• [?] Code review guidelines
• [-] Merge request performance guidelines
• [?] Style guides
• Database guides
• Separation of EE specific content