Mark purchase order as fetched or viewed

Please be aware about the following when using this endpoint:

1. Please use the fields with their correct scopes in mind:
   1. fetched_by_supplier: This field is intended to used internally by the supplier in order to enable filtering which orders have already been fetched in the Get Supplier Purchase Orders endpoint. This field is meant to be used exclusively by the supplier and does not provide any feedback to our mutual customers.
   2. viewed_by_supplier: Used to acknowledge the order was received by the supplier. When the order is set as viewed, the customer receives an order status update on their Apicbase account. This means the customer expects the order to be processed by the supplier and that it will either be delivered on the requested date or that the supplier will communicate any possible issues.
2. This endpoint will also set the respective timestamps fetched_by_supplier_at and viewed_by_supplier_at to the current time.
3. It is not possible to revert these fields back to false after they've been set to true, so be careful when using this endpoint.