[bug] position field broken with children elements

[signebedi]

[bug] position field broken with children elements
Currently, when we create children, it still uses the standard position of the document based on the length of the total database.

    def create(self, data, parent_id=None):
        data['created_at'] = datetime.datetime.now()
        data['last_edited'] = datetime.datetime.now()
        data['position'] = self.collection.count_documents({}) + 1  # Assign the next position
        if parent_id is not None:
            data['parent_id'] = parent_id  # Add the parent_id to the document
        return self.collection.insert_one(data).inserted_id

We need to change this such that, if parent is not null, we use different logic to determine position.

Originally posted by @signebedi in #9 (comment)