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/CompatibilityChecker.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace Mollie\Api;
+
+use Mollie\Api\Exceptions\IncompatiblePlatform;
+class CompatibilityChecker
+{
+    /**
+     * @var string
+     */
+    public const MIN_PHP_VERSION = "7.2";
+    /**
+     * @throws IncompatiblePlatform
+     * @return void
+     */
+    public function checkCompatibility()
+    {
+        if (!$this->satisfiesPhpVersion()) {
+            throw new \Mollie\Api\Exceptions\IncompatiblePlatform("The client requires PHP version >= " . self::MIN_PHP_VERSION . ", you have " . \PHP_VERSION . ".", \Mollie\Api\Exceptions\IncompatiblePlatform::INCOMPATIBLE_PHP_VERSION);
+        }
+        if (!$this->satisfiesJsonExtension()) {
+            throw new \Mollie\Api\Exceptions\IncompatiblePlatform("PHP extension json is not enabled. Please make sure to enable 'json' in your PHP configuration.", \Mollie\Api\Exceptions\IncompatiblePlatform::INCOMPATIBLE_JSON_EXTENSION);
+        }
+    }
+    /**
+     * @return bool
+     * @codeCoverageIgnore
+     */
+    public function satisfiesPhpVersion()
+    {
+        return (bool) \version_compare(\PHP_VERSION, self::MIN_PHP_VERSION, ">=");
+    }
+    /**
+     * @return bool
+     * @codeCoverageIgnore
+     */
+    public function satisfiesJsonExtension()
+    {
+        // Check by extension_loaded
+        if (\function_exists('extension_loaded') && \extension_loaded('json')) {
+            return \true;
+        } elseif (\function_exists('json_encode')) {
+            return \true;
+        }
+        return \false;
+    }
+}