解决RabbitMQ SimpleMessageConverter only supports String, byte[] and Serializable payloads

RabbitMQ 和 Spring Boot 整合，使用 rabbitTemplate.convertAndSend 方法发送消息到队列时，报如下错误：

java.lang.IllegalArgumentException: SimpleMessageConverter only supports String, byte[] and Serializable payloads, received: gy.finolo.springbootmybatisplus.entity.Order

	at org.springframework.amqp.support.converter.SimpleMessageConverter.createMessage(SimpleMessageConverter.java:161)
	at org.springframework.amqp.support.converter.AbstractMessageConverter.createMessage(AbstractMessageConverter.java:88)
	at org.springframework.amqp.support.converter.AbstractMessageConverter.toMessage(AbstractMessageConverter.java:70)
	at org.springframework.amqp.support.converter.AbstractMessageConverter.toMessage(AbstractMessageConverter.java:58)
	at org.springframework.amqp.rabbit.core.RabbitTemplate.convertMessageIfNecessary(RabbitTemplate.java:1758)
	at org.springframework.amqp.rabbit.core.RabbitTemplate.convertAndSend(RabbitTemplate.java:1075)
	at gy.finolo.springbootmybatisplus.producer.OrderSender.send(OrderSender.java:19)
	at gy.finolo.springbootmybatisplus.rabbitmq.RabbitMQTest.testSend(RabbitMQTest.java:27)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:675)
	at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
...

是因为 Order 这个类没有实现 implements Serializable 接口。