[EKS] [CoreDNS]: Ability to select/provide CoreDNS image used in managed CoreDNS EKS Addon

**Tell us about your request**
A capability to either select from a series of supported CoreDNS images or provide a reference to an arbitrary CoreDNS image in the EKS-managed CoreDNS addon.

**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?**
We're currently investigating different options for cross-cluster service discovery using the MCS API.
According to your own [AWS Cloud Map MCS controller intro post](https://aws.amazon.com/blogs/opensource/introducing-the-aws-cloud-map-multicluster-service-controller-for-k8s-for-kubernetes-multicluster-service-discovery/), a new CoreDNS image is required to use the `multicluster` [CoreDNS plugin](https://coredns.io/explugins/multicluster/).
I've validated this is still the case with the current provided version of EKS-managed CoreDNS.
This exact case could be solved by adding the `multicluster` plugin to the EKS CoreDNS standard image, but I think a more generic solution would be helpful to the community.

**Are you currently working around this issue?**
Run a separate unmanaged CoreDNS instance with the required addons and use a forward rule for the `clusterset.local` domain using a [custom Corefile](https://repost.aws/knowledge-center/eks-conditional-forwarder-coredns).
This is fine for development/low volume but introduces additional complexity and point of failure.

Start with the EKS-managed CoreDNS addon requirements, the linked AWS Cloud Map MCS controller introduction, and the CoreDNS multicluster plugin documentation. Compare those requirements with the current workaround using a separate CoreDNS instance and custom Corefile; done means defining a supported or arbitrary CoreDNS image selection path for the managed addon.

Written by the indexing model from the issue text.