Add klarna acknowledge order subcriber

packages/medusa-payment-klarna/src/subscribers/order.js

@@ -0,0 +1,14 @@
+class OrderSubscriber {
+  constructor({ klarnaProviderService, eventBusService }) {
+    this.klarnaProviderService_ = klarnaProviderService
+
+    this.eventBus_ = eventBusService
+
+    this.eventBus_.subscribe("order.completed", async (order) => {
+      const klarnaOrderId = order.payment_method.data.id
+      await this.klarnaProviderService_.acknowledgeOrder(klarnaOrderId)
+    })
+  }
+}
+
+export default OrderSubscriber