✨(backend) add max ancestors role field to document access endpoint

This field is set only on the list view when all accesses for a given
document and all its ancestors are listed. It gives the highest role
among all accesses related to each document.

src/backend/core/models.py

@@ -1140,7 +1140,9 @@ class DocumentAccess(BaseAccess):
                 set_role_to.append(RoleChoices.OWNER)
 
         # Filter out roles that would be lower than the one the user already has
-        ancestors_role_priority = RoleChoices.get_priority(ancestors_role)
+        ancestors_role_priority = RoleChoices.get_priority(
+            getattr(self, "max_ancestors_role", None)
+        )
         set_role_to = [
             candidate_role
             for candidate_role in set_role_to