Mongo integration uses deprecated collStats command

[zoehneto]

When upgrading to Mongo 6.2 or later, you receive regular warnings in the Mongo log stating The collStats command is deprecated. For more information, see https://dochub.mongodb.org/core/collStats-deprecated. This is due to usages of the collStats command in the Mongo integration. The suggested replacement by Mongo (using the $collStats aggregation stage) is possible since Mongo 3.4, so shouldn't break backwards compatibility.