2024-03-25: GPT-4 environment variables

You can now specify your GPT model name and version entirely in the azd environment variables. See updated documentation here:
https://github.com/Azure-Samples/azure-search-openai-demo/blob/main/docs/deploy_features.md#using-gpt-4

What's Changed

• Fix search secret name environment variable for free deploys by @pamelafox in #1455
• Allow manual setting of the OpenAI Deployment Name, Version, Capacity and Model by @john0isaac in #1386

Full Changelog: 2024-03-20...2024-03-25