OrderItem Improvements

This API update includes changes to the OrderItem object to improve usability and flexibility. Statuses can now freely be set to cover use cases such as substitutions or returns. Alongside this change, references also had their restrictions removed, enabling more seamless order revisions. Please refer to the changelog for specifics.

Previously, when using the `createOrderItem` mutation a unique `ref` was required. In alignment with `updateOrder`, this mutation now supports non-unique `ref` values and the restriction has been removed. This is helpful when performing tasks such as order revision for new order items to be added as you can now freely specify a ref number. 

Removed restricted values for the `status` field on the `OrderItem` entity. Enabling greater flexibility to set meaningful status information, such as "substituted", "returned", "replaced", or "cancelled".