Add popover to pipeline user - UX adjustment

What does this MR do and why?

UX adjustment for pipeline details header refactor (behind flag pipeline_details_header_vue). Display user popover for the user that triggered the pipeline.

First MR: !120634 (merged)

Second MR: !121174 (merged)

Third MR: !122216 (merged)

Fourth MR: !122516 (merged)

Design can be found here #394768[Unbox-pipeline-detail-page.png]

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable pipeline_details_header_vue in the rails console
2. Visit a pipeline
3. Hover over user name in the header section

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #394768 (closed)