FulfilmentItem Improvements

In this API release the flexibility of the FulfilmentItem has been improved. A list of attributes can now be stored and the status field has been unrestricted. Both of which allow for better storage of your custom information.

• Added extensibility to the `FulfilmentItem` entity by adding the standard `attributes` array field. This allows custom data fields and information, such as product serial numbers captured during packing, to be stored in the platform.
• Removed restricted values for the `status` field on the `FulfilmentItem` entity. Enabling greater flexibility to set meaningful status information, such as "substituted", "returned", "replaced", or "cancelled".