Summary

This will help to consolidate the implementation.

Currently there is a custom code for communicating with the A2A agents, instead it should use the a2a repository which contains an ADK for both clients and server. All we care about is the client - replace the custom code with the ADK client.

AC's

• The custom code in the local a2a/client.go package is replaced with the dedicated adk client from inference gateway - https://github.com/inference-gateway/a2a
• Redundant comments are removed
• The a2a/client.go is easier to maintain
• There are less sub functions - consolidate the implementation by reducing unnecessary function calls
• The a2a middleware still works as expected