Resolve "Make exam a many to many field on StudentInfo model"

core/serializers/submission_type.py

core/signals.py

core/templates/index.html

core/tests/test_access_rights.py

core/tests/test_assignment_views.py

core/tests/test_configuration_viewset.py

core/tests/test_export.py

core/tests/test_factory.py

core/tests/test_feedback.py

core/tests/test_labels.py

core/tests/test_student_page.py

core/tests/test_student_reviewer_viewset.py

core/tests/test_tutor_api_endpoints.py

core/views/common_views.py

core/views/export.py

frontend/package-lock.json

frontend/src/api.ts

frontend/src/components/BaseLayout.vue

frontend/src/components/CorrectionStatistics.vue

frontend/src/components/LabelStatistics.vue