Add e2e test: push mirroring over HTTP

What does this MR do?

Adds an end-to-end test of push mirroring a repository over HTTP.

This test will be replicated to cover pull mirroring and push/pull over SSH.

EE port: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8491

What are the relevant issue numbers?

For subsequent tests: https://gitlab.com/gitlab-org/gitlab-ce/issues/52576 gitlab-qa#344 (moved)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.