private ZoneEndpoint zoneEndpoint(ConfigModelContext context, ClusterSpec.Id cluster) {
        return context
                .getApplicationPackage()
                .getDeploymentSpec()
                .zoneEndpoint(context.properties().applicationId().instance(),
                              context.getDeployState().zone(),
                              cluster,
                              context.featureFlags().useNonPublicEndpointForTest());
    }
Add nodes to cluster according to the given containerElement.

Note: DO NOT change allocation behaviour to allow version X and Y of the config-model to allocate a different set
of nodes. Such changes must be guarded by a common condition (e.g. feature flag) so the behaviour can be changed
simultaneously for all active config models.
config-model/src/main/java/com/yahoo/vespa/model/container/xml/ContainerModelBuilder.java