Enrich commits with full data in CommitCollection (EE)

What does this MR do?

This MR contains cherry-picked commits from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26445 plus a commit that fixes broken ee tests.

What are the relevant issue numbers?

• https://gitlab.com/gitlab-org/gitlab-ee/issues/10567
• https://gitlab.com/gitlab-org/gitlab-ce/issues/58805

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• 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
• EE specific content should be in the top level /ee folder