Provide an option to send requests to grpups with max #active documents

[nehajatav]

Is your feature request related to a problem? Please describe.
When multiple groups are without full coverage, all but the worst will be used (by design). This means that if I have 2 unhealthy groups and 1 healthy group, it will result in only one group with worst coverage excluded resulting in query still going to other group with less than 100% coverage when the third group is available to serve requests with 100% coverage.

Describe the solution you'd like
An option to specify that searches should choose groups with #active documents same as max #active documents across groups