Python: Add GitHub Copilot BYOK sample

[droideronline]

Motivation & Context

GitHub Copilot supports BYOK (Bring Your Own Key — https://docs.github.com/en/copilot/how-tos/copilot-sdk/auth/byok), letting requests be routed through a custom OpenAI/Azure/Anthropic-compatible endpoint instead of the default GitHub Copilot backend. GitHubCopilotOptions.provider already forwards a ProviderConfig straight through to the Copilot SDK, but there was no sample demonstrating the scenario end-to-end.

Description & Review Guide

• What are the major changes? Adds github_copilot_with_byok.py under python/samples/02-agents/providers/github_copilot/, showing how to set GitHubCopilotOptions(model=..., provider=ProviderConfig(...)) to route through a custom endpoint, reading BYOK_BASE_URL/BYOK_API_KEY/BYOK_MODEL_ID from the environment. Updates the folder's README.md table to list the new sample.
• What is the impact of these changes? Documentation/sample only — no changes to library code.
• What do you want reviewers to focus on? Whether the ProviderConfig fields used (type, base_url, api_key, wire_api, model_id) match current guidance, and whether the security note on static BYOK credentials is clear enough.

Verified with ruff check, ruff format --check, and pyright (all clean).

Related Issue

Fixes #

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change.

[Copilot]

Pull request overview

Adds a new Python sample demonstrating how to use GitHubCopilotAgent with Copilot SDK BYOK (Bring Your Own Key) to route requests through a custom OpenAI/Azure/Anthropic-compatible endpoint, and documents it in the provider samples README.

Changes:

• Add github_copilot_with_byok.py sample showing BYOK configuration via GitHubCopilotOptions(provider=...) and environment variables.
• Update the GitHub Copilot provider samples README.md to include the new sample in the examples table.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
python/samples/02-agents/providers/github_copilot/README.md	Adds the BYOK sample to the examples list for discoverability.
python/samples/02-agents/providers/github_copilot/github_copilot_with_byok.py	New end-to-end sample configuring BYOK provider routing and model selection via env vars.

Comments suppressed due to low confidence (1)

python/samples/02-agents/providers/github_copilot/github_copilot_with_byok.py:41

• The sample hard-codes type: "openai" while the docstring claims Azure OpenAI/Anthropic are supported, and it also passes model_id inside ProviderConfig (the repo’s existing ProviderConfig examples/tests only use keys like type, base_url, api_key/bearer_token). This is likely to be rejected by the Copilot SDK or confuse users; keep the model selection at GitHubCopilotOptions(model=...) and let the provider type be configurable.

        "type": "openai",
        "base_url": os.environ["BYOK_BASE_URL"],
        "api_key": os.environ["BYOK_API_KEY"],
        "wire_api": "completions",
        "model_id": model_id,