add auth_provider param to support get_bearer_token_provider and custom auth headers

[kristapratico]

• I understand that this repository is auto-generated and my pull request may not be merged

Changes being requested

Example usage for Azure:

from openai import OpenAI
from azure.identity import get_bearer_token_provider, DefaultAzureCredential

client = OpenAI(
    base_url="https://resource.openai.azure.com/openai/v1",
    auth_provider=get_bearer_token_provider(
        DefaultAzureCredential(),
        "https://cognitiveservices.azure.com/.default"
    ),
    default_query={"api-version": "preview"}
)

Example usage for custom auth headers:

from openai import OpenAI

def get_auth_headers():
    ...
    return {"header1": "value", "header2": "value"}

client = OpenAI(
    auth_provider=get_auth_headers
)

Additional context & links