Get rid of dummy value used to parse mongodb CollectionId

In MongoDbIncrementalSnapshotChangeEventSource constructor and other places the parsing of the CollectionId is using a dummy value "UNUSED":

this.signallingCollectionId = connectorConfig.getSignalingDataCollectionId() == null ? null
: CollectionId.parse("UNUSED", connectorConfig.getSignalingDataCollectionId());

Find a way to get rid of the dummy value