Multicluster instructions fail due to kustomize versioning

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# Summary

The multicluster instructions fail with newer versions of kubectl / kustomize.

# Problem

The multicluster instructions rely on a kustomize command to install a sample app:
https://github.com/linkerd/website/blob/6fb58af2b803fa3fe96d95e052fe5c0571caced4/linkerd.io/content/2-edge/tasks/multicluster.md?plain=1#L283-L290

Unfortunately this does not work with kustomize 5 / kubectl 1.27+:

```bash
$ kubectl --context=${ctx} apply \
-n test -k "github.com/linkerd/website/multicluster/${ctx}/"
error: invalid Kustomization: json: cannot unmarshal string into Go struct field Kustomization.patches of type types.Patch
```

... due to the multicluster sample app's kustomize config format:
https://github.com/linkerd/website/blob/6fb58af2b803fa3fe96d95e052fe5c0571caced4/multicluster/west/kustomization.yml

Note `podinfo` using the new format:
https://github.com/stefanprodan/podinfo/blob/33dac1ba40f73555725fbf620bf3b4f6f1a5ad89/kustomize/kustomization.yaml

Switching to kubectl `v1.26.12` mostly works around the problem, but still partially fails due to HPA versioning:

```bash
$ curl -sfL -o ./kubectl-v1.26.12 https://storage.googleapis.com/kubernetes-release/release/v1.26.12/bin/linux/amd64/kubectl
$ chmod a+x ./kubectl-v1.26.12

$ ./kubectl-v1.26.12 --context=${ctx} apply \
-n test -k "github.com/linkerd/website/multicluster/${ctx}/"
error: resource mapping not found for name: "podinfo" namespace: "" from "github.com/linkerd/website/multicluster/west/": no matches for kind "HorizontalPodAutoscaler" in version "autoscaling/v2beta1"
ensure CRDs are installed first
```

# Proposal

Update the files under https://github.com/linkerd/website/blob/6fb58af2b803fa3fe96d95e052fe5c0571caced4/multicluster/ to use the new kustomize format.

# My environment

```bash
$ kubectl version
Client Version: v1.29.0
Kustomize Version: v5.0.4-0.20230601165947-6ce0bf390ce3
Server Version: v1.27.3
```

Start with content/2-edge/tasks/multicluster.md and the manifests under multicluster/, especially multicluster/west/kustomization.yml. Compare their format with the linked podinfo example, then run the documented kubectl apply -k command using current kubectl/Kustomize versions. Done means the sample app applies successfully without the patches or HorizontalPodAutoscaler errors.

Written by the indexing model from the issue text.