fix: multi client in direct mode

[HuJingKang]

问题: 直连模式下如果有多个客户端的话，所有客户端都会订阅第一个客户端的数据，导致数据错乱

const { NacosConfigClient } = require('nacos');

const dataId = 'dataId';
const group = 'group';

const client1 = new NacosConfigClient({
  serverAddr: '127.0.0.1:8848',
  namespace: 'local',
});
client1.subscribe({ dataId, group }, data => {
  console.log('client1', data);
});

const client2 = new NacosConfigClient({
  serverAddr: '127.0.0.1:8848',
  namespace: 'test',
});
client2.subscribe({ dataId, group }, data => {
  console.log('client2', data);
});

const client3 = new NacosConfigClient({
  serverAddr: '127.0.0.1:8849',
  namespace: 'test',
});
client3.subscribe({ dataId, group }, data => {
  console.log('client3', data);
});

经排查，NacosConfigClient 中的 clusterOptions.name 是由 endpoint 构成的，如果没有传 endpoint 的话，name 都会是 DiamondClient@undefined。所以直连模式下，所有的name都相同, 第一个client是Leader，后面所有的client都是第一个client的Follower，所以订阅的都是第一个client的数据

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[ugrg]

这个问题我查下来，像是client使用默认的端口是7777，同建立多个client时，这个7777端口会被占用导致失效。
不过好在我们可以使用NODE_CLUSTER_CLIENT_PORT这个环境变量来设置默认端口，这样就可以避免多个服务使用同一个接口而链接失败。实践下来，将这个值设置成0,即可实现随机端口。