add is_monday_start option to course creation and cloning.

[shishiro26]

NOTE: Please review the pull request process before opening your first PR: https://github.com/WikiEducationFoundation/WikiEduDashboard/blob/master/CONTRIBUTING.md#pull-request-process

#5689

What this PR does

This PR adds the is_monday_start flag to the course model, allowing the system to track whether a course follows a Monday–Sunday or a Sunday–Saturday schedule.

Screenshots

Before: https://github.com/user-attachments/assets/eb5b308f-9f44-424d-8c24-6d05ed832123 After:

course creation https://github.com/user-attachments/assets/c972ef0b-ba9b-4ab9-beb6-b8afea4e3a86

course cloning

https://github.com/user-attachments/assets/d966ed36-bb5a-4a1f-bc05-4882749bcb97