Added reviewer drawer component

What does this MR do and why?

Adds a reviewer drawer component that will show the reviewers, and approval rules for the merge request.

#448423 (closed)

MR acceptance checklist

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

Screenshots or screen recordings

How to set up and validate locally

• Enable reviewer_assign_drawer feature flag
• Visit a merge request
• Click Edit button in reviewer sidebar