Djoser v3 - use only GenericAPIView as a base

[tomwojcik]

APIView doesn't have serializer_class attribute. serializer_class is needed to generate OpenAPI spec with drf-spectacular. WDYT about not using APIView in v3, only generics.GenericAPIView or something higher level?

Overall I don't think we should be mixing APIViews and GenericAPIView. @GrbavaCigla do you think using only GenericAPIView as the base makes sense?

./views.py:30:class TokenDestroyView(views.APIView):
./webauthn/views.py:32:class SingupRequestView(APIView):
./webauthn/views.py:53:class SignupView(APIView):
./webauthn/views.py:96:class LoginRequestView(APIView):
./webauthn/views.py:127:class LoginView(APIView):

Token destroy - empty serializer, qs settings.TOKEN_MODEL.objects.none()
webauthn - all use different models and serializers