fix: A2A RPC URL got overriden by host and port param of adk api server

[copybara-service]

fix: A2A RPC URL got overriden by host and port param of adk api server

[racinmat]

Hi, could anyone please explain how to expose agents defined in ADK over A2A that I want to deploy to various places?
I need to have the url as a parameter, because if I deploy ADK agent somewhere, and expose it over A2A, then the URL needs to correspond to where it's deployed which can't be hardcoded in a json file, because obviously, the same source code will be deployed to different environments accessible under different URLs.

[racinmat]

I am fixing this in #2556 .