NodeJS Message router implementation

Hello,

My goal is to ensure a consumer will always receive key associated messages.
But from my tests, on adding/removing consumers there are cases where Pulsar will do a rebalance.

So I think my best shot is to publish to a specific partition and subscribe to this specific partition with my customer.

So what I would do is implement the Message Router interface [as explained here](https://pulsar.apache.org/docs/3.0.x/concepts-messaging/#routing-modes).
But I could not make it in the Node.js client, as it does not seem to exist.

Will that be implemented in the future ?

Let me know if I'm mistaking or if it's unclear, as I'm pretty new to Apache Pulsar.
Thanks for reading.

首先阅读链接的 Pulsar 路由模式文档，然后检查 Node.js 客户端中的 Producer APIs，以及任何现有的 Message Router 接口或路由测试。当客户端提供所请求的 message-router 行为，并支持将带键消息路由到目标分区且不会发生不必要的重新平衡时，即视为完成。

由索引模型根据 Issue 内容生成。