Support model -> deployment name mapping

[agladysh]

I'm using several models in my code, with a deployment for each, so we can't use config.deploymentName.

Azure doesn't allow . character in deployment names.

I have to send gpt-35-turbo to Azure and gpt-3.5-turbo to OpenAI.

Currently I have to change model my createChatCompletion code, depending on the provider.

It would be great to be able to provide a model to deployment mapping (dictionary or a callback) in the azure-openai configuration instead.