Splitting chunks for zone violations must not impact scalability

Within the balancer round we are checking if any chunk needs to be split due to zone violations. The aim of this ticket is to reduce the amount of time this check takes in case of having a large number of collections.

A proposal is to modify the selectChunksToSplit implementation and perform a query joining config.tags and config.chunks to find the chunks violating zones instead of bringing to memory all the zones and all the collection distributions.