[new][based on reverted project]admin can send join link to new instructors

1. redo the changes to the reverted project
2. now by default sample data will be imported for new instructor
3. modify the joinCourseForInstructor method to handle both instructors added by admin and other instructors
I realize it is legacy code. It is still not good. The method is doing more than what the name suggests. either give a better name to the method or (preferred) refactor the method to do only one thing.