A2A + Kafka

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

Hello! Would be nice to have a demo about how to set up A2A with Kafka using A2A Python SDK. Could something like that be part of this samples repository? Thank you very much

### Describe the solution you'd like

Inspired this blog about ["Why Google’s Agent2Agent Protocol Needs Apache Kafka"](https://www.confluent.io/blog/google-agent2agent-protocol-needs-kafka/)

### 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

Look at existing A2A Python SDK samples in the repository to understand the structure. Research how to integrate Kafka with the A2A protocol, referencing the linked blog post. The goal is to create a new Jupyter Notebook demo showing the setup, likely in a new directory. Check for any existing Kafka-related code or configurations in the repo.

由索引模型根據 Issue 內容生成。