Blob refactor: Display pipeline editor button

What does this MR do and why?

Display a Pipeline Editor button when viewing a .gitlab-ci config file.

Note: changes in this MR is part of a bigger effort to refactor the blob viewer and is behind the refactor_blob_viewer feature flag.

Screenshots or screen recordings

before	after

How to set up and validate locally

1. Enable the refactor FF

   Feature.enable(:refactor_blob_viewer)

2. Create a .gitlab-ci file

3. Open the .gitlab-ci file

4. Notice the pipeline editor button in the blob header

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 #342681 (closed)