fix: add websocket url option and fix example

[l4mby]

In this PR we add an option to specify the websocket url directly and we fix the websocket_example.js

const environment = rabbit.createEnvironment({
    host: rabbitHost,
    port: rabbitPort,
    username: rabbitUser,
    password: rabbitPassword,
    webSocket: WebSocket,
    webSocketUrl: "ws://localhost:15678/ws"
  })

[ansd]

Thank you!

I can confirm that starting Tanzu RabbitMQ:

tanzu-rabbitmq$  make run-broker PLUGINS="rabbitmq_web_amqp"

followed by

rabbitmq-amqp-js-client/examples$ npm run rebuild-source && npm run websocket-example

works now.