Expose Exchange Internals to Improve Developer Experience

[Akamaozu]

Situation

• rabbitmq sends messages to exchanges using a connection + channel system
• jackrabbit communicates with rabbitmq instances using amqplib's connection and channel api
• jackrabbit's exchange does not expose amqplib's channel

Problem

• jackrabbit users are unable to handle channel-specific events / errors
  (see: https://amqp-node.github.io/amqplib/channel_api.html#channel_events)

Proposal

• expose amqplib's channel so jackrabbit developers can go deeper than jackrabbit's interface allows, if need be
• use a similar api as jackrabbit client instance
  (see: https://github.com/pagerinc/jackrabbit/blob/7fb2afc5ffbf71c330e88c877a7735b71d1c61eb/lib/jackrabbit.js#L205-L214)