Feature Request: use dotenv for environment variables as well

So far, I need to put variables in `.env` and some shell needs extra `export` like

```bash
export OPENAI_API_KEY=sk-e5b67baxxx
```

It will be nice to use `dotenv` to load `.env` file when started to avoid extra steps for the environment setting

see [.env.sample](https://github.com/Azure/azure-openai-samples/blob/main/.env.sample) which is kind of common nowadays

thx.