[EKS] [request]: Specify CNI version when provisioning a cluster

**Tell us about your request**
EKS automatically installs the latest supported versions of the CNI, kube-proxy, and core-dns when a cluster is provisioned, however, there are times when using the latest version of these components will have unintended consequences. Customers should be allowed to specify which version of the CNI they want to use at provision time.

**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?**
Customers may have developed automation that relies on certain behaviors. If those behaviors change their automation may break.

**Are you currently working around this issue?**
How are you currently solving this problem?
Updating the automation after an incident (reactive rather than proactive)

**Additional context**
Anything else we should know?

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

The request concerns EKS cluster provisioning and selecting a CNI version, but it names no repository file, test, or implementation entry point. Start by determining whether EKS exposes a provisioning API for this choice and where this roadmap request is tracked; done means customers can select a supported CNI version at cluster creation without relying on reactive automation updates.

Written by the indexing model from the issue text.