Add Mollie API integration and webhook for software upgrade payments

- Introduced the `CaBundle.php` class for managing CA certificates.
- Updated `installed.json` and `installed.php` to include the new `composer/ca-bundle` dependency.
- Added `platform_check.php` to enforce PHP version requirements.
- Created `initialize.php` for initializing the Mollie API client with the API key.
- Implemented `webhook_mollie.php` to handle webhook callbacks for software upgrade payments, including transaction status updates and invoice generation.
- Integrated DomPDF for generating invoices and sending them via email.

assets/mollie/src/Endpoints/OrderRefundEndpoint.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace Mollie\Api\Endpoints;
+
+use Mollie\Api\Resources\Order;
+use Mollie\Api\Resources\Refund;
+use Mollie\Api\Resources\RefundCollection;
+class OrderRefundEndpoint extends \Mollie\Api\Endpoints\CollectionEndpointAbstract
+{
+    protected $resourcePath = "orders_refunds";
+    /**
+     * Get the object that is used by this API endpoint. Every API endpoint uses one type of object.
+     *
+     * @return Refund
+     */
+    protected function getResourceObject()
+    {
+        return new \Mollie\Api\Resources\Refund($this->client);
+    }
+    /**
+     * Get the collection object that is used by this API endpoint. Every API endpoint uses one type of collection object.
+     *
+     * @param int $count
+     * @param \stdClass $_links
+     *
+     * @return RefundCollection
+     */
+    protected function getResourceCollectionObject($count, $_links)
+    {
+        return new \Mollie\Api\Resources\RefundCollection($this->client, $count, $_links);
+    }
+    /**
+     * Refund some order lines. You can provide an empty array for the
+     * "lines" data to refund all eligible lines for this order.
+     *
+     * @param Order $order
+     * @param array $data
+     * @param array $filters
+     *
+     * @return Refund
+     * @throws \Mollie\Api\Exceptions\ApiException
+     */
+    public function createFor(\Mollie\Api\Resources\Order $order, array $data, array $filters = [])
+    {
+        return $this->createForId($order->id, $data, $filters);
+    }
+    /**
+     * Refund some order lines. You can provide an empty array for the
+     * "lines" data to refund all eligible lines for this order.
+     *
+     * @param string $orderId
+     * @param array $data
+     * @param array $filters
+     *
+     * @return \Mollie\Api\Resources\Refund
+     * @throws \Mollie\Api\Exceptions\ApiException
+     */
+    public function createForId($orderId, array $data, array $filters = [])
+    {
+        $this->parentId = $orderId;
+        return parent::rest_create($data, $filters);
+    }
+}