Update JS implementation to ES6 JavaScript Modules and External Services

Hello, I noticed the legacy JavaScript implementation in the plugin.

Please consider updating the implementation to use JavaScript Modules with ES6. For guidance, you can refer to the following documentation:

• Moodle JavaScript Guide
• JavaScript Modules in Moodle
• Ajax

Additionally, please consider updating the AJAX implementation to use External Services. For guidance, you can refer to the following documentation:

• External Services
• Writing a new service

This approach offers improved security and ensures better compatibility with Moodle standards.