Removed detached prefix from mr pipelines

What does this MR do and why?

Related to #372445 (closed) - we recently removed the detached mr state/label in favour of just merge request.

This MR updates the backend used to feed the MR widget amongst other things.

Screenshots or screen recordings

Before:

It looks like there are still quite a few references to detached in the codebase/frontend. Anyone involved on this issue would mind chiming in on a new issue: #372445 (comment 1088066274)

After:

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Create a simple project with a simple .gitlab-ci.yml:

   something:
     script: echo hello
     rules:
       - if: $CI_MERGE_REQUEST_IID

2. Create a new branch and push a commit

You should see the detached wordage if you're on master (see screenshot above).

If you're on this branch, you should no longer see the detached wordage.

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.