Add audit event for status checks must succeed setting

What does this MR do and why?

Add audit event for status checks must succeed setting

Creates new audit event when only_allow_merge_if_all_status_checks_passed column of project settings is updated, closing a compliance gap where a privileged user could silently disable external status checks on merge requests without leaving an audit trail.

References

• #602263

Screenshots or screen recordings

How to set up and validate locally

1. Ensure you have an EE license installed in GDK
2. Switch to the feat/add-status-checks-must-succeed-audit-event branch
3. Create a project
4. Navigate to the project's Settings > Merge Requests and toggle Status checks must succeed on and and off
5. Navigate to the project's Secure > Audit Events and confirm the events are present

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.