Add customer_id as an attribute to order_detailed_serializer
Add customer_id as an attribute to order_detailed_serializer

Therefor customer_id will be available on the order object for `/api/v0/orders/[ORDER_ID].json` endpoint

mkllnk/openfoodnetwork,openfoodfoundation/openfoodnetwork,lin-d-hop/openfoodnetwork,openfoodfoundation/openfoodnetwork,openfoodfoundation/openfoodnetwork,mkllnk/openfoodnetwork,lin-d-hop/openfoodnetwork,lin-d-hop/openfoodnetwork,openfoodfoundation/openfoodnetwork,mkllnk/openfoodnetwork,mkllnk/openfoodnetwork,lin-d-hop/openfoodnetwork