Enable auto-scaling for "existing" AWS deployments

[iameskild]

The AWS AutoScaling feature is not included for “existing” deployments. As far as I can tell, the only input variable we need is the EKS cluster name: https://github.com/Quansight/qhub/blob/main/qhub/template/stages/02-infrastructure/aws/modules/kubernetes/autoscaling.tf

Without this enabled, new nodes will not be spun up automatically.