feat(core-flows,medusa,types): fulfillment API: create (#7101)

what:

- adds fulfillment create API

RESOLVES CORE-1962

integration-tests/modules/__tests__/fixtures/fulfillment/index.ts

@@ -30,7 +30,8 @@ export function generateCreateFulfillmentData(
       country_code: "test-country-code_" + randomString,
       province: "test-province_" + randomString,
       phone: "test-phone_" + randomString,
-      full_name: "test-full-name_" + randomString,
+      first_name: "test-first-name_" + randomString,
+      last_name: "test-last-name_" + randomString,
     },
     items: data.items ?? [
       {