feat (backend) : student classes

[michaelcoll]

• Add the student_class table #87
• Add the quiz_class_visibility table #88
• Update the user table to add a foreign key to student_class #89
• Create and update all db queries #91
• Add the GET /api/v1/class endpoint to list all classes #93
• Add the POST /api/v1/class endpoint to add a new class #95
• Add the DELETE /api/v1/class/{UUID} endpoint to delete a class #96
• Add the PUT /api/v1/class/{UUID} endpoint to update a class #97
• Add the POST /api/v1/user/{userId}/class/{UUID} endpoint to enroll a user to a class #99
• Add the POST /api/v1/quiz/{sha1}/class/{UUID} endpoint to make the quiz visible to the class students #100
• Add the DELETE /api/v1/quiz/{sha1}/class/{UUID} endpoint to remove the quiz visibility to the class students #101
• Update the GET /api/v1/quiz and GET /api/v1/quiz/{sha1} to restrain the visibility to the student #102
• Update openapi spec #103