feat(generic): make importer return a message on error

The Select2QuerysetView does not handle errors well. We override the
`post` method of the view, so we can catch exceptions and add an error
message to the response. Once the custom select2js is updated, the error
messge will be displayed in the select input field.

apis_core/generic/views.py

@@ -1,3 +1,4 @@
+from django import http
 from django.conf import settings
 from django.contrib.auth.mixins import PermissionRequiredMixin
 from django.views.generic import DetailView
@@ -246,6 +247,12 @@ def get_results(self, context):
     def create_object(self, value):
         return create_object_from_uri(value, self.queryset.model)
 
+    def post(self, request, *args, **kwargs):
+        try:
+            return super().post(request, *args, **kwargs)
+        except Exception as e:
+            return http.JsonResponse({"error": str(e)})
+
 
 class Import(GenericModelMixin, PermissionRequiredMixin, FormView):
     template_name = "generic/generic_import_form.html"