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/vendor/composer/installed.json

@@ -0,0 +1,85 @@
+{
+    "packages": [
+        {
+            "name": "composer\/ca-bundle",
+            "version": "1.3.6",
+            "version_normalized": "1.3.6.0",
+            "source": {
+                "type": "git",
+                "url": "https:\/\/github.com\/composer\/ca-bundle.git",
+                "reference": "90d087e988ff194065333d16bc5cf649872d9cdb"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https:\/\/api.github.com\/repos\/composer\/ca-bundle\/zipball\/90d087e988ff194065333d16bc5cf649872d9cdb",
+                "reference": "90d087e988ff194065333d16bc5cf649872d9cdb",
+                "shasum": ""
+            },
+            "require": {
+                "ext-openssl": "*",
+                "ext-pcre": "*",
+                "php": "^5.3.2 || ^7.0 || ^8.0"
+            },
+            "require-dev": {
+                "phpstan\/phpstan": "^0.12.55",
+                "psr\/log": "^1.0",
+                "symfony\/phpunit-bridge": "^4.2 || ^5",
+                "symfony\/process": "^2.5 || ^3.0 || ^4.0 || ^5.0 || ^6.0"
+            },
+            "time": "2023-06-06T12:02:59+00:00",
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-main": "1.x-dev"
+                }
+            },
+            "installation-source": "dist",
+            "autoload": {
+                "psr-4": {
+                    "_PhpScoperf7c63b60b99d\\Composer\\CaBundle\\": "src"
+                }
+            },
+            "notification-url": "https:\/\/packagist.org\/downloads\/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Jordi Boggiano",
+                    "email": "j.boggiano@seld.be",
+                    "homepage": "http:\/\/seld.be"
+                }
+            ],
+            "description": "Lets you find a path to the system CA bundle, and includes a fallback to the Mozilla CA bundle.",
+            "keywords": [
+                "cabundle",
+                "cacert",
+                "certificate",
+                "ssl",
+                "tls"
+            ],
+            "support": {
+                "irc": "irc:\/\/irc.freenode.org\/composer",
+                "issues": "https:\/\/github.com\/composer\/ca-bundle\/issues",
+                "source": "https:\/\/github.com\/composer\/ca-bundle\/tree\/1.3.6"
+            },
+            "funding": [
+                {
+                    "url": "https:\/\/packagist.com",
+                    "type": "custom"
+                },
+                {
+                    "url": "https:\/\/github.com\/composer",
+                    "type": "github"
+                },
+                {
+                    "url": "https:\/\/tidelift.com\/funding\/github\/packagist\/composer\/composer",
+                    "type": "tidelift"
+                }
+            ],
+            "install-path": ".\/ca-bundle"
+        }
+    ],
+    "dev": false,
+    "dev-package-names": []
+}