feat(apis_relations): update GenericTripleForm to work with generic uri

The `Uri` model now uses a generic foreign key instead of the direct
foreign key to the `RootObject`. This commit updates all occurences
of `root_object` to instead use the generic foreign key.

apis_core/apis_relations/forms.py

@@ -129,10 +129,11 @@ def load_subj_obj_prop(
         self.fields["property"].initial = property_initial_value
         self.fields["property"].choices = [property_initial_value]
 
+        content_type = ContentType.objects.get_for_model(entity_instance_other)
         other_entity_initial_value = (
             str(
-                Uri.objects.filter(
-                    root_object=entity_instance_other,
+                Uri.object.filter(
+                    content_type=content_type, object_id=entity_instance_other.id
                 ).first()
             ),
             f"<span ><small>db</small> {str(entity_instance_other)}</span>",