[EKS] [request]: Enable PodNodeSelector Admission Controller for EKS

**Tell us about your request**
It would be nice if it was possible to use PodNodeSelector in EKS.

**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?**
In our EKS clusters, we are looking to leverage namespaces to represent our deployment environments. In order to do this safely, we want to label different auto-scaling groups of nodes as production and non-production. We then could use have the clusterDefaultNodeSelector select the non-production nodes, and the prod namespace target production nodes.

**Are you currently working around this issue?**
We are currently considering 2 workarounds.
1. Having our CD pipeline inject a nodeSelector into each deployment manifest based on the namespace being deployed to.
2. Writing a MutatingAdmissionWebhook to handle node selection, but this seems like we would just be re-writing the built-in PodNodeSelector.

The issue provides no repository files, tests, or entry points. Start by reviewing the Kubernetes PodNodeSelector admission controller requirements and EKS's support for admission controllers, using the namespace and node-label scenarios described here. Done would mean EKS can safely provide the requested default and namespace-specific node selection behavior.

Written by the indexing model from the issue text.