Report the number of databases that have globally-aggregated metrics in the 'resourceConsumption' serverStatus section.

This information is already accessible by using the following aggregation pipeline:

> db.aggregate([{$operationMetrics: {}}, {$count: "num"}]);
{ "num" : 42 }

This comes from a Cloud request to put this diagnostic information in serverStatus for consumers that are already fetching the serverStatus periodically.