Provisioning needs a note about the amount of time

When provisioning an assignment, the modal dialog needs a note or some kind of feedback to let the user know a) that this may take a long time (~3 minutes for a class of 30 students) and b) that it's actually working (not "stuck").

<img width="1780" height="437" alt="Image" src="https://github.com/user-attachments/assets/01b64499-8dfb-48d8-9a8d-1ee512b977e6" />