Create flag for pipeline details header refactor - part 1

What does this MR do and why?

First MR in a series of MRs to move pipeline details into a Vue app. As well as introduce a new design as seen in #394768[Unbox-pipeline-detail-page.png]

This component will be merging app/assets/javascripts/pipelines/components/header_component.vue and the current HAML data together.

Screenshots or screen recordings

header	header

How to set up and validate locally

1. Enable pipeline_details_header_vue in the rails console
2. Visit a pipeline
3. View 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)