[Reports] Include sortable name for the gradebook_history_api.feed

[agschmid]

Currently, the gradebook_history_api.feed (https://canvas.instructure.com/doc/api/gradebook_history.html#method.gradebook_history_api.feed), (and actually all of the gradebook_history endpoints), contains names in the "first_name last_name" format. It would be very useful if sortable_name could be returned. When pulling this data for any kind of report, being able to alphabetize the list by "last_name, first_name" would be helpful.