Support for Open-AI compatible (e.G. Local/Self-Hosted Models)

Currently only the API key is a valid option for the OpenAI provider. Theoretically other OpenAI like APIs, e.G. LM-Studio, OLLAMA -- which could be self hosted -- also support image data as input, if vision enabled models are loaded. Being able to set the BASE_URL for the OpenAi provider seems to be an easy route to initially integrate and support local hosted models.