Add a `.env` parameter that allows users to define the default GPT version to be used by the application.
### ⚠️ Please check that this feature request hasn't been suggested before. - [X] I searched previous [Ideas in Discussions](https://github.com/reworkd/AgentGPT/discussions/categories/ideas) didn't find any similar feature requests. - [X] I searched previous [Issues](https://github.com/reworkd/AgentGPT/labels/enhancement) didn't find any similar feature requests. ### 🔖 Feature description There should be a .env parameter, which can define the default gpt version. ### ✔️ Solution Define a .env parameter which is used, e.g. openai_modell_version. ### ❓ Alternatives _No response_ ### 📝 Additional Context _No response_ ### Acknowledgements - [X] My issue title is concise, descriptive, and in title casing. - [X] I have searched the existing issues to make sure this feature has not been requested yet. - [X] I have provided enough information for the maintainers to understand and evaluate this request.