[Feat] Determine how to simplify configuration for A2A servers and clients when using Quarkus

[fjuma]

This is a large issue that will likely need to be broken down into sub-issues.

Things we should consider include:

• Avoid needing to specify the same configuration (e.g., host, port, etc.) in multiple places like application.properties and in the agent card producer
• Reduce the amount of boilerplate configuration required
• Simplify the configuration for A2A agents that behave as clients
• The above will likely involve better integration with the LangChain4j agentic module

Implementation-wise, we'll likely want to consider creating a Quarkus extension.

[fjuma]

Also see quarkiverse/quarkus-langchain4j#1895