Resolve "CI retry/cancel job or pipeline redirect the user and can't be open in a new tab"

What does this MR do?

Frontend

• Clean up CSS - reuse the same HTML & CSS between all dropdowns (Commit, MR widget, pipeline tables)
• Receive JSON in stage.vue

Backend

• @ayufan keep stage endpoint returning HAML for the HAML commit graph and stage.json returning json for MR widget & pipeline tables

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

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #33697 (closed)