Partially update attributes of a customer's order.

Currently only the tags field is supported. Tags are prepended in front
of the existing tags. Duplicates are removed case-insensitively, keeping
the first occurrence (new tags win). More fields will be added in future
iterations.

Required fields:

• customer_id
• order_id
• tags (non-empty list)

A successful request returns the order with the updated attributes.

This operation is only supported for Shopify integrations.