Document ChangeConsumer usage for Debezium Engine

When using the debezium engine and the ChangeConsumer, the definition for the ChangeConsumer must be MyChangeConsumer implements DebeziumEngine.ChangeConsumer<RecordChangeEvent<SourceRecord>> per  the documentation.

If would be nice if the ChangeConsumer supported other formats like Json.class.

We look at the ConvertingEngineBuilder.java in debezium-embedded and tried to implement code like in DebeziumEngine<R> build() for converting the record but was not successful when converting RecordChangeEvent<SourceRecord>.record().value() to json.