Add support for G5 instance class

[fortejas]

Why do you want this feature?

There's newly released G5 Instance Types. Would be great to be able to deploy these with eksctl.

[isaac-ward]

Hi fortejas - was this feature implemented? I am having some trouble using g5 instances - the EC2 instances spin up but the nodes never join the cluster and become ready in the nodegroup.

Is it possible to use g5 instances currently with EKSCTL?

[fortejas]

@isaac-ward I saw the same behavior but I think awslabs/amazon-eks-ami#806 is the more relevant issue rather than something not working with eksctl specifically