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/Onboarding.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace Mollie\Api\Resources;
+
+use Mollie\Api\Types\OnboardingStatus;
+class Onboarding extends \Mollie\Api\Resources\BaseResource
+{
+    /**
+     * @var string
+     */
+    public $name;
+    /**
+     * @var string
+     */
+    public $signedUpAt;
+    /**
+     * Either "needs-data", "in-review" or "completed".
+     * Indicates this current status of the organization’s onboarding process.
+     *
+     * @var string
+     */
+    public $status;
+    /**
+     * @var bool
+     */
+    public $canReceivePayments;
+    /**
+     * @var bool
+     */
+    public $canReceiveSettlements;
+    /**
+     * @var \stdClass
+     */
+    public $_links;
+    /**
+     * @return bool
+     */
+    public function needsData()
+    {
+        return $this->status === \Mollie\Api\Types\OnboardingStatus::NEEDS_DATA;
+    }
+    /**
+     * @return bool
+     */
+    public function isInReview()
+    {
+        return $this->status === \Mollie\Api\Types\OnboardingStatus::IN_REVIEW;
+    }
+    /**
+     * @return bool
+     */
+    public function isCompleted()
+    {
+        return $this->status === \Mollie\Api\Types\OnboardingStatus::COMPLETED;
+    }
+}