Modified sale line serialization for cart #7211

By default, the standard fields 'display_name', 'url', 'image' are
picked from the sale line's product. In downstream modules this
behaviour can be modified.

sale.py

@@ -164,6 +164,13 @@ def serialize(self, purpose=None):
         if purpose == 'cart':
             res.update({
                 'id': self.id,
+                'display_name': self.description or self.product.name,
+                'url': self.product.get_absolute_url(_external=True),
+                'image': (
+                    self.product.default_image.transform_command().thumbnail(
+                        150, 150, 'a'
+                    ).url() if self.product.default_image else None
+                ),
                 'product': self.product.serialize(purpose),
                 'quantity': number_format(self.quantity),
                 'unit': self.unit.symbol,