[GREEN] Modify new endpoints to refer to main id instead of revision id

apps/cases/migrations/0001_initial.py

apps/cases/models.py

apps/cases/serializers.py

apps/cases/tests/test_units/test_case_subjects.py

apps/cases/tests/test_units/test_investigation_cases.py

apps/cases/tests/test_units/test_monitoring_cases.py

apps/cases/tests/test_units/test_positive_cases.py

apps/cases/views.py

apps/commons/managers.py

project/settings.py