[EKS] allow dots in cluster names

**Tell us about your request**
I would like to use dots in my cluster names

**Which service(s) is this request for?**
EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
I am trying to reuse a lot of automation to migrate kops-created clusters to EKS clusters. kops allows clusters with dots, EKS does not

**Are you currently working around this issue?**
Replacing dots with dashes, and it's never truly clear when I'll get away without doing that.

This is an AWS EKS feature request motivated by migrating kops-created clusters and currently replacing dots with dashes. Start by reviewing the EKS cluster-name constraints and the existing kops-to-EKS automation; done means EKS accepts cluster names containing dots without requiring that workaround.

Written by the indexing model from the issue text.