Require additional approver on breaking changes that impact high-traffic operations

**Request**
Require additional approver on breaking changes that impact high-traffic operations.

**Use case**
Developers are often tweaking in-development APIs on production targets, and so it's useful to give them approver permissions to allow day-to-day changes, since often breaking or dangerous changes will go through without client impact. However, this sometimes leads to human error issues where a breaking change was approved because the developer may not have fully understood the warning from hive.

It would be helpful to have distinct permissions for approval that vary according to traffic threshholds, so that low-traffic breaking and dangerous changes approval permissions can be granted to everyone, whereas approving changes that impact high traffic could require another approver.