[Feat] Create a sample that makes use of multiple agents written with Quarkus LangChain4j

We have a sample that shows how agents written in different languages can collaborate with each other:

https://medium.com/google-cloud/multi-language-agent-collaboration-and-interoperability-with-a2a-e5fe80b4962d

We've had a request to create a sample where all of the agents are written with Quarkus LangChain4j so it's clear how an agent can send a request to an A2A server agent in this case.

This could probably also leverage the `langchain4j-agentic` module (note that this module still needs to be updated to the 0.3.0 version of the A2A Java SDK but that work is in progress):

https://github.com/langchain4j/langchain4j/blob/main/docs/docs/tutorials/agents.md?plain=1#L1154

The idea would be to add this sample to https://github.com/a2aproject/a2a-samples