Automatically remove attention requested state

What does this MR do and why?

This automatically removes the users attention request if one of the following actions happens:

• Approve a merge request
• Add someone else as a reviewer or assignee
• Request attention from another reviewer or assignee

The attention request is also removed from all reviewers and assignees if the merge request is closed or merged.

Screenshots or screen recordings

How to set up and validate locally

Enable the mr_attention_requests feature flag.

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.

Closes #345365 (closed)