Python: Add middleware sample to show filtering messages between agents

[moonbox3]

Summary

Add middleware sample for message interception between agents.

Files

File	Line
sample: group_chat_agent_manager.py	before GroupChatBuilder

Context

# TODO: think about using middleware to help filter messages between agents
workflow = (
    GroupChatBuilder()
    .with_agent_orchestrator(orchestrator_agent)

Use cases: content filtering, message transformation, access control between agents.

Action Items

• Design middleware interface for message interception
• Document use cases and patterns