OpenAI: add config baseUrl for gateways

[hotlong]

Is your feature request related to a problem? Please describe.
Yes, I cannot config gateway for OpenAI : https://developers.cloudflare.com/ai-gateway/providers/openai/

Describe the solution you'd like
Add config or as an env var

Describe alternatives you've considered
none

Additional context

Cloudflare Example:

import OpenAI from 'openai';

const openai = new OpenAI({
	apiKey: 'my api key', // defaults to process.env["OPENAI_API_KEY"]
	baseURL: "https://gateway.ai.cloudflare.com/v1/{account_id}/{gateway_slug}/openai"
});

try {
  const chatCompletion = await openai.chat.completions.create({
    model: "gpt-3.5-turbo-0613",
    messages: [{ role: "user", content: "What is a neuron?" }],
    max_tokens: 100,
  });

  const response = chatCompletion.choices[0].message;

  return new Response(JSON.stringify(response));
} catch (e) {
  return new Response(e);
}

[hotlong]

https://github.com/openai/openai-node/blob/master/src/index.ts

opts.baseURL=process.env['OPENAI_BASE_URL'] ?? https://api.openai.com/v1] - Override the default base URL for the API.

[hotlong]

Environment variables don't work; it seems like environment variables cannot be accessed when running in sandbox mode.

[emengweb]

need that too

[hotlong]

should add an environment variable to control which environment variables a piece can access during its execution.