fix(core-flows): export registerOrderDeliveryStep (#12221)

Export registerOrderDeliveryStep to ensure devs can use it and to show it in the docs

.changeset/tidy-cheetahs-train.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/core-flows": patch
+---
+
+fix(core-flows): export registerOrderDeliveryStep

packages/core/core-flows/src/order/steps/index.ts

@@ -21,6 +21,7 @@ export * from "./exchange/create-exchange"
 export * from "./exchange/create-exchange-items-from-actions"
 export * from "./exchange/delete-exchanges"
 export * from "./preview-order-change"
+export * from "./register-delivery"
 export * from "./register-fulfillment"
 export * from "./register-order-changes"
 export * from "./register-shipment"