To define a storage interface for getOperationStatistics method.
To implement this interface for WiredTiger storage engine.

Suggestion:
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1. Storage interface could be RecoveryUnit::getOperationStatistics(bool reset)
2. WiredTiger method could be WiredTigerRecoveryUnit::getOperationStatistics(bool reset).

WiredTiger implementation will open a session statistics cursor, fetches the statistics from WiredTiger session and returns them as a BSON object.

Whether this will return the BSON object if any of the statistics is zero ? need to be discussed with NY.