Update order signal enum handling

AWAITING_SHIPMENT_CREATION is removed from OrderSignalNameEnum. Remove it from requests and saved API filters; requests using a removed enum value fail validation.

Responses can include the categories ISSUES, TO_DO, and INFORMATION, and the signal FULFILLMENT_BLOCKED. Update exhaustive enum handling. The older category values remain accepted while both sets are in use. Held orders continue to use the on_hold order status.