Support for user parameter in OpenAI Embeddings Create class, which exists in OpenAI API

[sujithjoseph]

Feature request

https://platform.openai.com/docs/api-reference/embeddings/create?lang=python supports a user parameter, where we can pass user details to the openai api. https://github.com/hwchase17/langchain/blob/master/langchain/embeddings/openai.py#L66 can take a user parameter (optional) , which needs to be passed via embed_with_retry function.

Motivation

We use it to track user details - could be appkey etc.

Your contribution

Yes, can create a PR. Please let me know process .