Properly handle channel errors

Per https://github.com/Surnet/graphql-amqp-subscriptions/pull/13/files#r422921589 , we should handle channel errors by attempting to re-establish them when possible. https://github.com/guidesmiths/rascal is a good example to go off of.

[chdanielmueller]

Connection errors should not be handled.
I think this is something the user of this library should handle.
We could bubble up an error but everything else seems wrong since it could cause errors if we change something on the shared connection.

Channel error handling an reestablishing those could be worth it.
Maybe even only use one instead of two channels. (Publish and Subscribe use one each)
But the combining of those channels should be discussed and well researched.

Throwing another library in that I have been recommended to use in a scenario like this:
https://www.npmjs.com/package/amqp-connection-manager
For sure needs evaluation which one to use.

@chdanielmueller Good call, forgot the connection was passed in. This would only be for channel errors. Title and description updated.