Add ``<mods:identifier>`` with `uuid`.

def add_uuid(dom, uuid):
    """
    Add ``<mods:identifier>`` with `uuid`.
    """
    mods_tag = get_mods_tag(dom)

    uuid_tag = dhtmlparser.HTMLElement(
        "mods:identifier",
        {"type": "uuid"},
        [dhtmlparser.HTMLElement(uuid)]
    )

    insert_tag(uuid_tag, dom.find("mods:identifier"), mods_tag)