Cancel Consumer and Restart

[rphansen91]

Issue
Currently it is possible to cancel a consumer, but their is not clear way to restart the consumer.

Reason
When dependencies of a Microservice are offline it is beneficial to stop the consumer and only restart when work is ready to be continued. This saves a lot of rabbit bandwidth not needing to deliver nack requeue over and over until the consumer is ready.

Solution
Maintain a list of the consumer options so that the canceled consumer can be restarted

[craigotis]

@underfisk This feature seems to meet one of our service needs - but I'm finding it hard to retrieve the ConsumerTag created once a subscriber is established. The AmqpConnection.createSubscriber() method returns Promise<void>, so it's unclear what we're supposed to pass to the cancel/resume functions to make use of this. 🤔

[underfisk]

@craigotis Would you be down to have a PR to fix this issue?

[craigotis]

@underfisk I'm happy to look into it - though it seems the subscription is created in the addSetup() callback for the ChannelWrapper from this project, so it would potentially need to be implemented as an optional callback parameter in the createSubscriber() function.

Before I go that route though, am I missing something? How was this cancel/restart implementation intended to be used?

Edit: It might look something like this: #472

[underfisk]

@craigotis Your PR looks good to me but i would advocate adding some test coverage so that we can safely track whether its properly working