@Override
        public AthenzDomain tenantSecretDomain() {
            if (tenantSecretDomain.isEmpty())
                throw new IllegalArgumentException("Tenant secret domain is not set for zone " + zone);
            return AthenzDomain.from(tenantSecretDomain);
        }
Returns the host provisioner to use, or empty to use the default provisioner,
creating hosts from the application package defined hosts
configserver/src/main/java/com/yahoo/vespa/config/server/deploy/ModelContextImpl.java