Mention CoreDNS autoscaling via addon

[niallthomson]

What would you like to be added?

The Cluster Proportional Autoscaling section should mention that this scenario can now be covered with the EKS CoreDNS addon:

https://docs.aws.amazon.com/eks/latest/userguide/coredns-autoscaling.html

This should be a header or something at the start of the lab.

Why is this needed?

Currently the lab might suggest this approach is the recommended approach, whereas customers should likely start with the EKS addon.