Add GitHub Copilot client

GitHub Copilot Chat in the Visual Studio Code already support Model Context Protocol (MCP).

It is recommended to add GitHub Copilot to the [Example Clients](https://modelcontextprotocol.io/clients) page.

See also: [Extending Copilot Chat with the Model Context Protocol (MCP)](https://docs.github.com/en/copilot/customizing-copilot/extending-copilot-chat-with-mcp)


