Add identifier count vs property count to the stats

[Sadads]

With the addition of the new tracking of identifiers, can you generate a metric for the use of identifiers per the availability of the data at: https://phabricator.wikimedia.org/T114617 . This would be super useful for communicating how our impact effects the semantic/linked-open web to partners: https://phabricator.wikimedia.org/T114617