Update to use Api V2 of Open ai Assistants

Problem/Motivation

The module does not work with the latest models created with the use of the latest version (2) of the api.

Steps to reproduce

Try to switch for example to gpt-4o model and an error appears:
OpenAI\Exceptions\ErrorException: The requested model 'gpt-4o' cannot be used with the Assistants API in v1. Follow the migration guide to upgrade to v2: https://platform.openai.com/docs/assistants/migration. in OpenAI\Transporters\HttpTransporter->throwIfJsonError() (line 131 of /app/vendor/openai-php/client/src/Transporters/HttpTransporter.php).

Proposed resolution

There is a migration guide to v2 of the Assistants API https://platform.openai.com/docs/assistants/migration

Remaining tasks

Implement the required changes.

User interface changes

API changes

Data model changes