create-cluster.sh produces error "field dnsSearch not found in type v1alpha4.Networking"

*Description*:

The create-cluster.sh includes a configuration item (dnsSearch) that doesn't exist for the Cluster apiVersion.
https://github.com/envoyproxy/gateway/blob/main/tools/hack/create-cluster.sh#L25-L27

*Repro steps*:

create-cluster.sh will fail to create a cluster, with the output:

> ERROR: failed to create cluster: unable to decode config: yaml: unmarshal errors:
> line 8: field dnsSearch not found in type v1alpha4.Networking
>

Removing `dnsSearch` from Cluster.networking fixes it.

*Environment*:

main branch