Resolve: "Pipelines: When we retry a pipeline 2 requests are made to the pipelines endpoint"

What does this MR do?

When the user clicks on retry or cancel, server should send 204 response.

Changes made:

• Frontend makes HTTP request with content-type: 'application/json'
• Backend send 204 for JSON

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
  • 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 #30237 (closed)