2022-12-14 — Add flow_id to application state

Adds the flow_id field to the application state returned from most Checkout Frontend and Backend endpoints.

The flow_id is an identifier for the origin checkout flow that created the order. Bold-hosted templates provide this field and are identified by the first 4 letters "bold", which are reserved. The field is optional for custom checkout flows and other clients, but provides a convenience for determining the order's origin.