Move Autoscaling content

[niallthomson]

There are two issues with the current "Autoscaling" top level section:

1. Karpenter is not strictly autoscaling, and given its scope probably belongs in Fundamentals
2. It takes up a top nav bar section for little content

This section should be re-distributed around the Fundamentals section.

1. Cluster Autoscaler lab should be moved under the Managed Node Groups section
2. Karpenter lab should be moved to a top level lab under Fundamentals, along side the existing MNG group
3. Workload autoscaling labs should be moved to a top level group under Fundamentals called "Workload autoscaling"

We should add redirects to the new pages for the benefit of existing links.