Issue #3003349 by kaszarobert, mirom: Add submodule with example implementation

/admin/commerce/config/superfaktura

```

Next step is to create own module with subscriber to call SuperFaktura service.

Next step is to set when should the invoice creating service run. If you want to send invoices just when the order was placed, then enable the **superfaktura_invoice_place** submodule.

Otherwise create an own module with subscriber to call SuperFaktura service.

In example below SuperFaktura service is called when Order is placed.

```

<?php

namespace Drupal\superfaktura_invoice_place\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;

use Drupal\state_machine\Event\WorkflowTransitionEvent;

/**

 * Superfaktura event subscriber.

 */

class SuperfakturaSubscriber implements EventSubscriberInterface {

  /**

   * {@inheritdoc}

   */

  public static function getSubscribedEvents() {

    return [

      'commerce_order.place.pre_transition' => ['createInvoice', -200],

    ];

  }

  /**

   * Create Invoice in Superfaktura from created order.

   *

   * @param \Drupal\state_machine\Event\WorkflowTransitionEvent $event

   *   Transition Event.

   */

  public function createInvoice(WorkflowTransitionEvent $event) {

    /** @var \Drupal\commerce_order\Entity\Order $order */

    $order = $event->getEntity();

    /** @var \Drupal\superfaktura\InvoiceService $invoice */

    $invoice = \Drupal::service('superfaktura.invoice_service');

    $invoice->createInvoice($order);

  }

}

name: Superfaktura Invoice Place Example Integration

type: module

description: Sample integration module that creates a Superfaktura invoice when an order is placed.

package: Commerce

core_version_requirement: ^8 || ^9

dependencies:

  - state_machine:state_machine

services:

  superfaktura_invoice_place.event_subscriber:

    class: Drupal\superfaktura_invoice_place\EventSubscriber\SuperfakturaSubscriber

    tags:

      - { name: event_subscriber }