[EKS] [request]: No client-ca-file in extension-apiserver-authentication configmap

**Tell us about your request**
Currently, if you spin up a new EKS cluster, the extension-apiserver-authentication configmap does not include the client-ca-file.

I would like the client-ca-file to be included in the extension-apiserver-authentication configmap by default so you don't manually have to inject it into new clusters.

**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?**
Tools such as Certificate Manager or Metrics Server requires this to work.

It is possible to manually get the client-ca-file through the AWS CLI and then manually inject it, but it is very cumbersome.

The client-ca is available per default in both GKE and AKS.

**Are you currently working around this issue?**
I am currently working around the issue by getting the certificate through the AWS CLI:

```
aws eks describe-cluster \
--region=${AWS_DEFAULT_REGION} \
--name=${CLUSTER_NAME} \
--output=text \
--query 'cluster.{certificateAuthorityData: certificateAuthority.data}' | base64 -D
```

Then I inject it into the extension-apiserver-authentication configmap manually:

```
kubectl -n kube-system edit cm extension-apiserver-authentication
```

Start by checking the EKS extension-apiserver-authentication ConfigMap and the AWS CLI workaround described in the issue. Done means new EKS clusters include client-ca-file by default, without manual injection, and tools such as Certificate Manager or Metrics Server can use it.

Written by the indexing model from the issue text.