Support for embeddings endpoint

### Description

Reference: https://platform.openai.com/docs/guides/embeddings

Would be helpful for building agents with indexes. Since authentication is already handled, having a one stop shop for all the APIs properly typed in Golang would be nice.

Something like this: https://github.com/charmbracelet/fantasy/commit/cbca0e58119d606e48f4b64dea3c92b217c97a74