Use AsyncEventingBasicConsumer in RabbitMQ

[mvelosop]

Use AsyncEventingBasicConsumer instead of EventingBasicConsumer to properly use async event handlers on consumers.

Taken from http://gigi.nullneuron.net/gigilabs/asynchronous-rabbitmq-consumers-in-net/

Closes #888.

As detected by @falamarzijahromi, the previous implementation was using async event handlers with EventingBasicConsumer (which isn't async) and this causes possible out-of-order message handling and improper exception handling. This is also explained in the above article.

Even though the ordering issue doesn't seem to affect eShopOnContainers it was fixed because it's not adecuate to synchronously call async event handlers.

However, the exception handling does affect the services, as will be shown next.

To create this situation you can now force an exception in the consumer, by including the text throw-fake-exception somewhere in the message, like this:

When placing the above order, the Ordering.API microservice aborts, as can be seen in the following images:

Processing just stops and alerts fire in health checks:

And the message gets stuck in the queue:

After applying the changes,

The exception is catched, logged and ignored as suggested in RabbitMQ's documentation:

NOTE: In a real-world application this situation should probably be handled with a Dead Letter eXchange (DLX).

After the error the service is still working and can process another order.