Backend code clean-up

[sampaccoud]

Feature Request

Is your feature request related to a problem or unsupported use case? Please describe. Our code has grown fast and could benefit come clean-up

Describe the solution you'd like

• [ ] Remove useless lookup_field = "pk" on viewsets
• [ ] Rename test methods to be homogeneous and self explanatory from generic to specific
• [ ] Rewrite admin API tests to use a staff user with minimal access rights instead of a superuser.
• [ ] Add admin API tests for an authenticated staff user without the required access rights and make sure they fail
• [ ] Make sure all API tests (admin and client) include read list, read detail, create, update, partial_update and delete, in that order
• [ ] Create a tree structure for test files as there are now too many in the core app. test_api_admin_contract_definitions.py will become tests/api/admin/contract_definitions.py
• [ ] Consider renaming serializer fields that only render an id to *_id e.g. product_id instead of product
• [ ] Extract logic from models and implement them in services (See marsha bbb utils)

Please add here anything that you noticed could be improved in the backend code.