[#26858] WIP - API for cctray pipeline project

What does this MR do?

Adds an API endpoint of

https://gitlab.com/api/v4/projects/2/pipelines/cc.xml

Returns Project XML according to the cctray standard https://github.com/erikdoe/ccmenu/wiki/Multiple-Project-Summary-Reporting-Standard which works on CCMenu.

Currently only support per project basis and takes the latest pipeline activity.

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

• Do we want to support multiple projects in a single call?

Why was this MR needed?

Adding feature for https://gitlab.com/gitlab-org/gitlab-ce/issues/26858

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?

https://gitlab.com/gitlab-org/gitlab-ce/issues/26858

Closes #26858 (moved)