[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