Kafka serializer for Akka ByteString

ByteStringSerializer.scala

    val byteStringSerializer = new org.apache.kafka.common.serialization.Serializer[ByteString]() {
      override def configure(configs: util.Map[String, _], isKey: Boolean): Unit = {}
      override def serialize(topic: String, data: ByteString): Array[Byte] = data.toArray
      override def close(): Unit = {}
    }