docs: add Microsoft Agent Framework integration guide (#716)

Covers using the Copilot SDK as a provider in MAF workflows including:
- Basic usage (wrapping CopilotClient as a MAF AIAgent)
- Custom function tools
- Multi-agent orchestration (sequential, concurrent)
- Streaming responses
- Configuration reference and best practices

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: patniko