feat(apis_entities): update AbstractEntity 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 use the generic foreign key instead.

apis_core/apis_entities/models.py

@@ -102,4 +102,9 @@ def create_default_uri(sender, instance, created, raw, using, update_fields, **k
                     "apis_core:GetEntityGeneric", kwargs={"pk": instance.pk}
                 )
             uri = f"{base}{route}"
-            Uri.objects.create(uri=uri, root_object=instance)
+            content_type = ContentType.objects.get_for_model(instance)
+            Uri.objects.create(
+                uri=uri,
+                content_type=content_type,
+                object_id=instance.id,
+            )