[BUG] Can't provide model to OpenAi constructor

[isaacwasserman]

Description

When instantiating mindsql.llms.OpenAi, the config parameter can only contain parameters to OpenAI's client constructor. This does not include model which must be passed to client.chat.completions.create. In MindSQL's OpenAi.invoke, the model parameter is expected to be in self.config, but it can't be.

Possible Solution

I think it's reasonable to include a model keyword param in the signature of the constructor. Otherwise, it could be removed from the input config prior to passing this config to the OpenAI client (this would avoid any breaking changes).