Clarify K8s service CIDR selection when using hybrid nodes

For hybrid nodes customers, the remote node and pod CIDRs can't conflict with the Kubernetes service CIDR. The default K8s service CIDR for EKS is 172.16.0.0/16 - we should state that in the hybrid nodes docs. We also need to clarify how the K8s service CIDR default is selected and whether a different CIDR is selected if you supply 172.16.0.0/16 for your remote node or pod CIDRs.