chore(eks): add private cluster reference link (#29201)

### Issue # (if applicable)



### Reason for this change

EKS cluster with isolated VPC has been a gap for customers and now we have a working reference architecture at https://github.com/aws-samples/aws-cdk-examples/tree/master/java/eks/private-cluster I am adding a link in the aws-eks README hopefully to have more visibility.



### Description of changes



### Description of how you validated changes



### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk-lib/aws-eks/README.md

@@ -657,7 +657,7 @@ new eks.Cluster(this, 'HelloEKS', {
 });
 ```
 
-> Note: Isolated VPCs (i.e with no internet access) are not currently supported. See https://github.com/aws/aws-cdk/issues/12171
+> Note: Isolated VPCs (i.e with no internet access) are not fully supported. See https://github.com/aws/aws-cdk/issues/12171. Check out [this aws-cdk-example](https://github.com/aws-samples/aws-cdk-examples/tree/master/java/eks/private-cluster) for reference.
 
 If you do not specify a VPC, one will be created on your behalf, which you can then access via `cluster.vpc`. The cluster VPC will be associated to any EKS managed capacity (i.e Managed Node Groups and Fargate Profiles).