Define custom fields and serializer for MatrixServiceProduct

uncloud/uncloud_pay/models.py

@@ -163,5 +163,9 @@ class Product(models.Model):
     def recurring_price(self, recurring_period=RecurringPeriod.PER_MONTH):
         pass # To be implemented in child.
 
+    @property
+    def setup_fee(self):
+        return 0
+
     class Meta:
         abstract = True