[SIS] Make enrollment status a "sticky" field for SIS uploads

[reynlds]

Problem statement:

Enrollment changes made in the GUI such as completing a student enrollment do not survive subsequent SIS file uploads if the student is identified in the feeder file as being enrolled in the course/section. In other words, the SIS upload resets the student in the course to "active".

Proposed solution:

When a Teacher makes an enrollment change in a course such as completing or deleting a student enrollment, that change should survive an SIS enrollment file upload if the override_sis_stickiness parameter is enabled on the upload. This will require having the "status" column of an enrollments CSV be reconfigured as a "sticky" field. https://canvas.instructure.com/doc/api/file.sis_csv.html There are a number of reasons that this is necessary including SIS processing delays, student/teacher conferences, etc.

User role(s):

admin,instructor,ta