[Feature]: Use models endpoint to automatically update model selection in chat node

### Feature Request

Open AI has an endpoint to get the models. Why are we not using this in the models selection for the Chat node?
This should ensure that preview models etc. are always available in the selection.

https://platform.openai.com/docs/api-reference/models/list

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct

Start with the Chat node's model-selection entry point and review the OpenAI Models API list endpoint linked in the issue. Determine how the returned models should populate the selection, including preview models, and verify that the available choices update as intended.

Written by the indexing model from the issue text.