A new field `orphanCount` has been added to the collStats aggregation stage output which represents the number of orphan documents in a collection

Description of Linked Ticket

With the introduction of ranges, chunks distribution will become much less meaningful to evaluate whether a collection is balanced or not.

Objective of this ticket is to return orphans as part of the collStats aggregation stage's output so that users can rely on some new metric to evaluate the balancing status.

To get the actual size of a collection on a shard, some example of metrics may be dataSize - orphansSize or countDocuments - countOrphans.