Add semi-sync support to replication API

The replication API supports the normal asynchronous replication. Adding support for semi-synchronous replication would guarantee that the transaction is committed only if the event is consumed.

The most reliable and versatile way would be to expose a function that sends the acknowledgement of the replicated event to the master. Another option would be to automatically send the aknowledgement when the event is received but this would still leave it vulnerable for crashes before the event is fully processed.