[Permissions] Prohibit observer accounts for staff

Problem statement:

Teachers currently have the ability to generate a pairing code for someone to observe their account on Canvas. Observers should NOT be permitted for anyone enrolled in a course as an Admin or Teacher. We allow self-registration and the use of pairing codes to support parent access to the activity on Canvas of their child(ren). However, the addition of a user as an observer of a staff member is an open loophole that needs to be closed.

Proposed solution:

If a user is enrolled in a course with the role of Admin or Teacher, observing is NOT permitted. Another option is to prohibit observing a staff profile (based on SIS contains staff_ or email contains @dvusd.org).

User role(s):