Add model parameter to openai.New() about langchaingo

[obitech]

This can be closed I guess? See #78

[cduggn]

Is it a necessity that the embedding model be an environment variable? These will be a finite set of values that could be defined as consts. Taking embeddings.NewOpenAI as an example, there is a need to provide an embedding name however that detail is somewhat hidden in the creation of the openai.New() struct which is called internally in the function and there is no comment which indicates the API Token and model are prerequisites

[tmc]

Is it a necessity that the embedding model be an environment variable? These will be a finite set of values that could be defined as consts. Taking embeddings.NewOpenAI as an example, there is a need to provide an embedding name however that detail is somewhat hidden in the creation of the openai.New() struct which is called internally in the function and there is no comment which indicates the API Token and model are prerequisites

There's a balance here between making the default high level API as simple as possible. I'm taking cues from upstream on this front.

The openai.WithModel() option enables this so I'm considering it closed. Please feel free to raise any discussion or propose any changes.

[tmc]

(To clarify, this was fixed in #78)