🧠 Provide an env var for `OPENAI_MODEL_NAME`

[jacobmyoung]

The initialization of configureOpenAIProvider is only sending the base url param, but will handle a default model name if provided. Following the existing pattern of the env var OPENAI_API_KEY, adding OPENAI_MODEL_NAME would allow a custom model to be set.

[jacobmyoung]

Thank you!