docs: Set ami_type for AL2023 in the example (#3337)

set ami_type for AL2023

Set AMI type explicitly   into user data type to be able to use cloudinit_pre_nodeadm 

https://github.com/terraform-aws-modules/terraform-aws-eks/blob/master/modules/_user_data/main.tf#L33

examples/eks-managed-node-group/eks-al2023.tf

@@ -20,6 +20,7 @@ module "eks_al2023" {
     example = {
       # Starting on 1.30, AL2023 is the default AMI type for EKS managed node groups
       instance_types = ["m6i.large"]
+      ami_type       = "AL2023_x86_64_STANDARD"
 
       min_size = 2
       max_size = 5