mod_cluster proxies doesn't accept expressions

proxy-list was deprecated in WFLY-457

Now I'm forced to use proxies but it doesn't accept expressions.

I want to create a customisable Docker image with where the modcluster ip can be configured at runtime

I'd like that Wildfly image to accept the following command but

/subsystem=modcluster/mod-cluster-config=configuration:write-attribute(name=proxies,value=[${modcluster.host:modcluster}:${modcluster.port:80}])}}

but if fails with: "Services that may be the cause:" => ["jboss.outbound-socket-binding.\"${modcluster.host:modcluster}:${modcluster.port:80}\""]

With

/subsystem=modcluster/:add-proxy(host=${modcluster.host:modcluster},port=80)

it fails with WFLYMODCLS0016: No IP address could be resolved for the specified host of the proxy.