Fix stray pipelines API request when showing MR

What does this MR do?

When showing a MR (/group/project/merge_requests/x), it doesn't hit the pipelines API unless specifically on the pipelines tab.

Are there points in the code the reviewer needs to double check?

• As an alternative solution... Should we get rid of the server-side rendering of the pipelines list and associated bundle and instead bootstrap it ourselves in merge_request_tabs.js.es6?
  • Pass in endpoint via the tab-pane data attribute

Why was this MR needed?

Previously, when showing a MR, it would hit the pipelines API regardless if you were on that tab or not.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Tests
  • 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 #27925 (closed)