Add back kustomize support
Add back kustomize support

This was removed in
https://github.com/kubernetes-sigs/service-apis/pull/274.

This breaks 1 line installation of CRDs used by a few demos already like
`kubectl apply -k 'github.com/kubernetes-sigs/service-apis/config/crd'`

istio/gateway-api,istio/gateway-api,istio/gateway-api