Add 'Hostname' enum val to k8s NodeAddress type.

Class io.fabric8.kubernetes.api.model.NodeAddress.type contains 'InternalIP','ExternalIP' and 'Hostname'. The InternalIP address is unavailable in the private cloud environment. But the hostname can be resolved by the DNS server. So 'org.apache.flink.kubernetes.configuration.NodePortAddressType.NodePortAddressType' should add 'Hostname' enumeration value.

//org.apache.flink.kubernetes.configuration.NodePortAddressType.NodePortAddressType
    public enum NodePortAddressType {
        InternalIP,
        ExternalIP,
        Hostname
    }