Added approval summary header to reviewer drawer component

What does this MR do and why?

Added approval summary header to reviewer drawer component

#448425 (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 merge request
• Click Edit button in reviewer sidebar widget