Add MR approval status to MR compliance entity

What does this MR do?

As part of the work for #217939 (closed) we need to surface the approval status to the frontend.

This MR adds the approval status checks to the MR compliance entity which is then given to the dashboard via JSON.

The checks are:

• MR authors are not allowed to approve MRs
• MR committers are not allowed to approve MRs
• The number of required approvers is >= 2

:success means that all of the above are true

:warning means that some of the above are true

:failed means that none of the above are true

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

1. Navigate to groups/[GROUP]/-/security/compliance_dashboard
2. Use the Vue pane in your dev tools if you have it and check the ComplianceDashboard components mergeRequests property
3. Alternatively you can use view source and check for instances of approval_status

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related #217939 (closed)