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/Resources/Capture.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace Mollie\Api\Resources;
+
+class Capture extends \Mollie\Api\Resources\BaseResource
+{
+    /**
+     * Always 'capture' for this object
+     *
+     * @var string
+     */
+    public $resource;
+    /**
+     * Id of the capture
+     * @var string
+     */
+    public $id;
+    /**
+     * Mode of the capture, either "live" or "test" depending on the API Key that was used.
+     *
+     * @var string
+     */
+    public $mode;
+    /**
+     * Amount object containing the value and currency
+     *
+     * @var \stdClass
+     */
+    public $amount;
+    /**
+     * Amount object containing the settlement value and currency
+     *
+     * @var \stdClass
+     */
+    public $settlementAmount;
+    /**
+     * Id of the capture's payment (on the Mollie platform).
+     *
+     * @var string
+     */
+    public $paymentId;
+    /**
+     * Id of the capture's shipment (on the Mollie platform).
+     *
+     * @var string
+     */
+    public $shipmentId;
+    /**
+     * Id of the capture's settlement (on the Mollie platform).
+     *
+     * @var string
+     */
+    public $settlementId;
+    /**
+     * @var string
+     */
+    public $createdAt;
+    /**
+     * @var \stdClass
+     */
+    public $_links;
+}