Lab-2 message retry information incorrect. Addition of DLQ steps might also be beneficial

[michaelprice232]

In the following lab-2 guide:
https://async-messaging.workshop.aws/topic-queue-chaining-and-load-balancer/test-topic-queue-chaining-and-load-balancer/test-topic-queue-chaining-and-load-balancing.html#3-validate-the-message-reception

It reports:

You should also see some log entries, indicating a failed message processing. Shortly after, you should see the message redelivery from Amazon SNS and the successful message processing log entry.

In lab-2 we have configured SQS queues as subscribers to the SNS topics and so it isn't SNS re-sending the message, but the Lambda consumer keep retrieving and re-trying the message from the queue. It would be good to update the docs to avoid confusion.

Also - it might be beneficial to add steps for enabling a DLQ for one of the SQS queues, after we have updated the logic of one of the backend lambdas to always fail (to simulate a persistent message failure and how to handle them).