[User-Story] - Supervisor Agent: migrate from agent-as-tools to hand-off built-in pattern available in agent-framework

**Description**
Hand-off pattern is the preferred agents orchestration implementation for conversational assistants. agent framework recently provided a built-in implementation and we have the opportunity to provide a clean, simple to understand, more maintainable option compared to the current sub-optimal agents-as-tool implementation which required a couple of custom work and hacks to make it reliable.
This will also lay the foundation for more complex hand-off scenarios like:
- Hierarchical teams of supervisors

**Current Behavior**
Supervisor agent use custom agent-as-tools approach.

**Acceptance Criteria**
- [ ] Supervisor agent is re-implemented using hand-off pattern.
- [ ] Both synch and asynch chat conversation works without any regression bugs.

**Design Consideration**
Refactor the Supervisor agent to use agent framework hand-off orchestration. The current approach is based on single-turn one shot delegation.
Single turn hand-off orchestration sample: https://github.com/microsoft/agent-framework/blob/main/python/samples/getting_started/workflows/orchestration/handoff_simple.py

**Main affected modules and/or classes**
- https://github.com/Azure-Samples/agent-openai-python-banking-assistant/blob/main/app/copilot/app/agents/azure_chat/supervisor_agent.py
assistant/blob/main/app/copilot/app/agents/foundry/payment_agent_foundry.py
- https://github.com/Azure-Samples/agent-openai-python-banking-assistant/blob/main/app/copilot/app/agents/foundry/supervisor_agent_foundry.py

---
*Migrated from: https://github.com/Azure-Samples/agent-openai-python-banking-assistant/issues/4*

Inizia con l'esempio handoff_simple.py di Microsoft Agent Framework, quindi esamina app/copilot/app/agents/azure_chat/supervisor_agent.py, payment_agent_foundry.py e supervisor_agent_foundry.py. Confronta l'attuale flusso di agent-as-tools con il pattern di hand-off e verifica che le conversazioni di chat sincrone e asincrone funzionino senza bug di regressione.

Scritto dal modello di indicizzazione a partire dal testo della issue.