Switch to GitHub models API for embeddings requests

[garman]

The GitHub Models API now supports /embeddings. This PR switches over to using the GitHub Models API.

[Copilot]

Pull Request Overview

This PR switches from using the Azure AI inference endpoint to the GitHub Models API for embeddings requests. The change migrates all sample code and documentation to use the new GitHub Models API endpoint, which now supports embeddings functionality.

• Updates endpoint URLs from https://models.inference.ai.azure.com to https://models.github.ai/inference
• Adds user agent header to OpenAI client configuration for better API tracking
• Updates environment documentation to clarify required token permissions

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
samples/python/openai/multi_turn.py	Adds GitHub Models sample user agent header to OpenAI client
samples/python/openai/embeddings_getting_started.ipynb	Updates OpenAI base URL to GitHub Models API endpoint
samples/python/openai/embeddings.py	Changes endpoint from Azure AI to GitHub Models API
samples/python/mistralai/getting_started.ipynb	Updates endpoint URL to GitHub Models API
samples/python/azure_ai_inference/getting_started.ipynb	Changes endpoint to GitHub Models API
samples/python/azure_ai_inference/embeddings.py	Updates endpoint URL to GitHub Models API
samples/js/openai/embeddings.js	Changes endpoint from Azure AI to GitHub Models API
samples/js/azure_ai_inference/embeddings.js	Updates endpoint URL to GitHub Models API
cookbooks/python/llamaindex/rag_getting_started.ipynb	Updates OpenAI base URL to GitHub Models API
.env-sample	Adds clarification about required token permissions