[EKS] [request]: Allow feature gates to be set on master components

**Tell us about your request**
I would like to be able to set [feature gates](https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/) on master components such as the kube-apiserver, this would allow me to enable features early.

**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?**
Right now I can't enable feature gates on any master components, while I have a particular feature gate in mind I would like the general ability to toggle feature flags upon creating/updating a cluster. I understand that the feature gates enable alpha features, so I would simply note in the documentation and a warning upon any feature flag being set that using this feature can make your cluster unstable and all feature gates set should be throughly tested before releasing to production.

The particular feature gate is the `VolumeSnapshotDataSource` which is needed for the EBS CSI Driver's snapshotting feature.

**Are you currently working around this issue?**
I will deploy my own container to do the snapshotting myself.

The request concerns EKS master components and Kubernetes feature gates, with VolumeSnapshotDataSource needed for the EBS CSI Driver's snapshotting feature. Start with the linked Kubernetes feature-gates documentation; done would mean feature gates can be set when creating or updating an EKS cluster, with the requested warnings and documentation.

Written by the indexing model from the issue text.