Adds api and subscriber

packages/medusa-plugin-economic/src/subscribers/order.js

@@ -0,0 +1,13 @@
+class OrderSubscriber {
+  constructor({ economicService, eventBusService }) {
+    this.economicService_ = economicService
+
+    this.eventBus_ = eventBusService
+
+    this.eventBus_.subscribe("order.placed", async (order) => {
+      await this.economicService_.draftEconomicInvoice(order)
+    })
+  }
+}
+
+export default OrderSubscriber