protected byte[] onDataAppend(final long logIndex, final byte[] value,
                                  final WriteContext ctx) throws IOException, InterruptedException {
        ctx.finishJob();
        return value;
    }
Called before appending data entry.

@param logIndex the log index
@param value    the data value in log entry.
@return the new value
jraft-core/src/main/java/com/alipay/sofa/jraft/storage/impl/RocksDBLogStorage.java