After SERVER-88400, the aggregation stage $shardedDataDistribution no longer returns null for the fields numOwnedDocuments, ownedSizeBytes, and orphanedSizeBytes on a timeseries collection.

However, the field numOwnedDocuments returns the number of buckets instead of the number of documents. This is incorrect according to the name of the field.
Therefore, we've decided to keep the numOwnedDocuments field for time-series collection as null and add a new field called numOwnedBuckets, and do the same for numOrphanedDocs.

Note that it would be too expensive to get the actual number of documents from a timeseries collection; that's why we decided to keep them as `null` and add the new 'bucket' fields instead.