add_labels: label IDs to add to the specified message
remove_labels: label IDs to remove from the specified message
user_id: gmail user_id to access, special value of 'me' indicates the authenticated user.
Examples
## Not run:gm_modify_message(12345, add_labels ="label_1")gm_modify_message(12345, remove_labels ="label_1")# add and remove at the same timegm_modify_message(12345, add_labels ="label_2", remove_labels ="label_1")## End(Not run)