Returns, Fulfillments and more Product info for the customer-accounts API

[ShaunStarttin]

The customer-accounts API  currently doesn't have some key fields that make developing apps for the OrderStatus page awkward. It'd be great to understand if/when there will be "parity" with the Orders object in admin API. Effectively, I was hoping we'd have access to everything currently visible on the OrderStatus page, such as:

- returns

- fulfillments

- a Product node and product metafields

To fetch these fields for an order, we need to use the admin API, which doesn't scale well for customer-facing data and it can be hard to cache it.