[EKS] [request]: Disable anonymous-auth to kube-apiserver

**Tell us about your request**
Add the ability to pass the `--anonymous-auth=false` flag to the `kube-apiserver`. Passing in other arbitrary flags to the apiserver would also be nice, but not as necessary.

**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?**
Several attacks target `kube-apiserver` through anonymous auth. [Billion laughs](https://github.com/kubernetes/kubernetes/issues/83253) is a good example of a very recent attack that could be exploited by anonymous auth.

Disabling anonymous auth completely is a security best-practice and mitigates a whole class of attacks.

**Are you currently working around this issue?**
By keeping our clusters up-to-date with security fixes and protecting the endpoint URLs from public discovery. We could use private API endpoints, but this is complicated due to https://github.com/aws/containers-roadmap/issues/221

**Additional context**
n/a

**Attachments**
n/a

Start by reviewing the EKS request and the Kubernetes kube-apiserver --anonymous-auth=false flag, then check whether EKS exposes a supported apiserver configuration entry point. Done means EKS provides a documented way to disable anonymous authentication, with the behavior verified for affected clusters.

Written by the indexing model from the issue text.