[Gradebook] Add Subject Line when you Message All Unassigned Students in a Group Set

Problem statement:

When you Message All Unassigned Students in a Group Set in the People tool, you can not add a Subject. Canvas does not include a Subject either and the message reads as (No subject) in the Inbox.

Proposed solution:

Pleases add a Subject line to that message or, even better, allow users to add one. Thank you

User role(s):

instructor,designer