[Feature] Add support for other LLM models

Currently, the app only supports Gemini's Cloud API. Support for using OpenAI's ChatGPT, Groq or Cohere would be beneficial for users.

* [openai-kotlin](https://github.com/Aallam/openai-kotlin)
* [community libraries for OpenAI](https://platform.openai.com/docs/libraries/community-libraries)