OpenAI has officially deprecated these APIs, but I'll leave them in as long as the endpoints still work
The engines api is also deprecated, but I'll get to that when I add
model support.
If certain engines are timing out regularly, then OpenAiService needs a timeout parameter.
I also added a constructor that takes an OpenAiApi, and this will allow users to customize their api settings much more easily.
If we need more parameters later, I might add a builder for OpenAiService.
Based on feedback in https://github.com/TheoKanning/openai-java/issues/5
