Missing validation on instance_type

[g-iannelli]

There is no validation about the EKS node pool instance_type.

For example if you use a t3.micro instance that support max 4 pods, can't run all required daemonset pods.

The following pods seems to be installed always on each node:

Namespace	Daemonset
calico-system	calico-node
kube-system	aws-node
kube-system	aws-node-termination-handler
kube-system	ebs-csi-node
kube-system	kube-proxy
logging	infra-fluentbit
logging	systemd-common-host-tailer
monitoring	kube-proxy-metrics
monitoring	node-exporter

Checking the max pods described in the official eks ami repository, the following instance type should not be allowed considering the 9 infrastructure pods plus 1 for custom workloads

curl -sSL https://raw.githubusercontent.com/awslabs/amazon-eks-ami/master/files/eni-max-pods.txt | grep -v -e '^\s*#' | awk '$2 <= 10 {print "-", $1}'
- a1.medium
- c6g.medium
- c6gd.medium
- c6gn.medium
- c7g.medium
- d3.xlarge
- d3en.xlarge
- g4ad.2xlarge
- g4ad.xlarge
- is4gen.medium
- m1.small
- m6g.medium
- m6gd.medium
- m7g.medium
- r6g.medium
- r6gd.medium
- r7g.medium
- t1.micro
- t2.micro
- t2.nano
- t3.micro
- t3.nano
- t3a.micro
- t3a.nano
- t3a.small
- t4g.micro
- t4g.nano
- x2gd.medium