Separate additional reviewers from required approvals in Reviewers sidebar section
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=495409)
</details>
<!--IssueSummary end-->
Not all reviewers are required approvals.
However the way we currently present the reviewers, it looks like they are all needed for required approvals.

To fix this we will add a subheading called "Additional reviewers" to separate required approvals and extra reviewers.

This concept inspired by the approval button turns into "Approve additionally" after the required approvals were given.
- This split only happens when there are required approvals
- In the case of the only required is `Any eligible user`, is it possible to say that we list those reviewers as the people who given approvals as they come in. Any additional approvals given after X then they would be listed under into "Additional reviewers".
issue