@Override
    public ChangeStreamOffset createInitialOffset() {
        return new ChangeStreamOffset(currentBsonTimestamp());
    }
An change stream offset factory class create {@link ChangeStreamOffset} instance.
Copy from com.ververica:flink-connector-mongodb-cdc:2.3.0.
inlong-sort/sort-flink/sort-flink-v1.13/sort-connectors/mongodb-cdc/src/main/java/org/apache/inlong/sort/cdc/mongodb/source/offset/ChangeStreamOffsetFactory.java