Fix UnsupportedMediaType

[Theodrem]

We are getting an error while dispatch on the API. The error received is an error 500 with a sentry. When the error UnsupportedMediaType is raised, we have to return a response 400.

UnsupportedMediaType: Unsupported media type "" in request.
  File "django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "rest_framework/viewsets.py", line 125, in view
    return self.dispatch(request, *args, **kwargs)
  File "concrete_datastore/api/v1/views.py", line 1908, in dispatch
    data = self.request.data
  File "rest_framework/request.py", line 216, in data
    self._load_data_and_files()
  File "rest_framework/request.py", line 279, in _load_data_and_files
    self._data, self._files = self._parse()
  File "rest_framework/request.py", line 351, in _parse
    raise exceptions.UnsupportedMediaType(media_type)