(aws-eks): Apply folder k8s resources to existing cluster

It would be neat if we could add a folder filled with k8s resources to eks cluster.

```
kubectl apply -k "github.com/aws/eks-charts/stable/aws-load-balancer-controller//crds?ref=master"
```

### Use Case

I'm trying to add an ALB ingress controller to the EKS cluster. But right now cannot do that through CDK.
I need to add custom resource definitions present online.
**Source:** [AWS_EKS_INGRESS_GUIDE](https://docs.aws.amazon.com/eks/latest/userguide/alb-ingress.html)

```
kubectl apply -k "github.com/aws/eks-charts/stable/aws-load-balancer-controller//crds?ref=master"
```
### Proposed Solution

I'm not sure how to proceed with this.
Adding constructor props to select folder mode to KubernetesManifest class and similarly adding a prop to addManifest() function of @aws-cdk/aws-eks.Cluster class

---

This is a :rocket: Feature Request

Start by reading the KubernetesManifest class and the addManifest() entry point on @aws-cdk/aws-eks.Cluster. Compare the requested kubectl apply -k behavior with the existing CDK APIs and determine the intended constructor and method props. Done means an existing EKS cluster can apply a folder of remote Kubernetes resources through CDK.

Written by the indexing model from the issue text.