Correctly show pipeline creator & created_at

What does this MR do?

It shows the correct creator & create datetime for a pipeline on the show page, e.g. https://gitlab.com/gitlab-org/gitlab-ce/pipelines/6782973

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #29255 (closed)