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/Mandate.php

@@ -0,0 +1,89 @@
+<?php
+
+namespace Mollie\Api\Resources;
+
+use Mollie\Api\MollieApiClient;
+use Mollie\Api\Types\MandateStatus;
+class Mandate extends \Mollie\Api\Resources\BaseResource
+{
+    /**
+     * @var string
+     */
+    public $id;
+    /**
+     * @var string
+     */
+    public $status;
+    /**
+     * @var string
+     */
+    public $mode;
+    /**
+     * @var string
+     */
+    public $method;
+    /**
+     * @var \stdClass|null
+     */
+    public $details;
+    /**
+     * @var string
+     */
+    public $customerId;
+    /**
+     * @var string
+     */
+    public $createdAt;
+    /**
+     * @var string
+     */
+    public $mandateReference;
+    /**
+     * Date of signature, for example: 2018-05-07
+     *
+     * @var string
+     */
+    public $signatureDate;
+    /**
+     * @var \stdClass
+     */
+    public $_links;
+    /**
+     * @return bool
+     */
+    public function isValid()
+    {
+        return $this->status === \Mollie\Api\Types\MandateStatus::STATUS_VALID;
+    }
+    /**
+     * @return bool
+     */
+    public function isPending()
+    {
+        return $this->status === \Mollie\Api\Types\MandateStatus::STATUS_PENDING;
+    }
+    /**
+     * @return bool
+     */
+    public function isInvalid()
+    {
+        return $this->status === \Mollie\Api\Types\MandateStatus::STATUS_INVALID;
+    }
+    /**
+     * Revoke the mandate
+     *
+     * @return null|\stdClass|\Mollie\Api\Resources\Mandate
+     */
+    public function revoke()
+    {
+        if (!isset($this->_links->self->href)) {
+            return $this;
+        }
+        $body = null;
+        if ($this->client->usesOAuth()) {
+            $body = \json_encode(["testmode" => $this->mode === "test" ? \true : \false]);
+        }
+        $result = $this->client->performHttpCallToFullUrl(\Mollie\Api\MollieApiClient::HTTP_DELETE, $this->_links->self->href, $body);
+        return $result;
+    }
+}