Add seats to serializer
Add seats to serializer

edx/ecommerce,eduNEXT/edunext-ecommerce,edx/ecommerce,mferenca/HMS-ecommerce,mferenca/HMS-ecommerce,mferenca/HMS-ecommerce,edx/ecommerce,eduNEXT/edunext-ecommerce,edx/ecommerce,eduNEXT/edunext-ecommerce,eduNEXT/edunext-ecommerce