[EKS] [request]: make cors-allowed-origins flag configurable in EKS kube clusters

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**Tell us about your request**
Kubernetes supports a `cors-allowed-origins` flag, seen in code at https://github.com/kubernetes/apiserver/blob/release-1.14/pkg/server/options/server_run_options.go#L144, that allows the configuration of CORS domains. Would like to be able to set this value so that the Kubernetes APIs can be CORS compliant.

**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?**
Without CORS compliance in the Kubernetes APIs, any client side dashboards that we build (running exclusively in the user's browser, making API calls with that user's credentials instead of server side requests) will require a proxy to allow for CORS compliance to workaround the problem. Unfortunately, adding a proxy to the mix introduces the potential for replay attacks using data from the proxy.

**Are you currently working around this issue?**
Will be building a proxy for our internal use to force CORS compliance with these API calls.

**Additional context**
N/A

**Attachments**
N/A

Start with the Kubernetes server_run_options.go reference for the cors-allowed-origins flag, then investigate how EKS exposes Kubernetes API server configuration. Done means EKS users can configure allowed CORS origins for Kubernetes APIs without requiring a proxy; the issue does not name repository files or tests to run.

Written by the indexing model from the issue text.