Introduction
Classes implementing this interface may be registered as a subscriber and
receive log messages from the extension. This is similar to stream-based
debug logging (i.e. mongodb.debug)
except that trace-level log messages are not received.
As with stream-based logging, it is only possible to register a logger
globally using MongoDB\Driver\Monitoring\addSubscriber().
The extension is not able to distinguish log messages for individual
MongoDB\Driver\Manager objects.