Switch EKS cluster to managed node groups

[giorgiosironi]

EKS introduced managed node groups rather than having you create EC2 instances manually. This matches that GCP does, and is probably going to become a standard.

We create the workers indirectly through the eks Terraform module so I wonder how that would change.

Definition of Done:

• all workers nodes are managed
• no manually created autoscaling groups or other resources

Related

Tasks

[giorgiosironi]

/cc @BlueReZZ for possible inclusion in https://github.com/libero/publisher/milestone/35