[Feat]: Add Sample A2A Implementation using FastA2A with Pydantic AI Agents

### Is your feature request related to a problem? Please describe.

We need an example demonstrating how to create A2A implementation using [FastA2A](https://ai.pydantic.dev/a2a) services that are powered by [Pydantic AI Agents](https://ai.pydantic.dev/agents/)

### Describe the solution you'd like

An implementation of A2A using FastA2A and Pydantic AI agents capable of serving requests from clients using the A2A protocol.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

The issue asks for a sample implementation using FastA2A and Pydantic AI Agents. Start by reading the linked FastA2A and Pydantic AI Agents documentation to understand the A2A protocol and agent framework. Look at existing samples in the repository for structure. The implementation will involve creating a service that can handle A2A protocol requests, likely in a Jupyter notebook or Python script. 'Done' means a working example that others can run.

Escrita pelo modelo de indexação a partir do texto da issue.