add openai.api_base

[TheLime1]

relevent issue here : #331
i have an api key from i must use with openai.api_base : It is used to specify the endpoint for the API request
example :

import openai

openai.api_key = "API KEY"
openai.api_base = "API BASE LINK"`

another example in openai python lib

import openai
openai.api_type = "azure"
openai.api_key = "..."
openai.api_base = "https://example-endpoint.openai.azure.com"
openai.api_version = "2023-05-15"

# create a chat completion
chat_completion = openai.ChatCompletion.create(deployment_id="deployment-name", model="gpt-3.5-turbo", messages=[{"role": "user", "content": "Hello world"}])

# print the completion
print(completion.choices[0].message.content)