Expose max_llm_calls to ADK web

In the runtime config, there is [max_llm_calls](https://google.github.io/adk-docs/runtime/runconfig/#max_llm_calls) setting. There is no mechanism to propagate this to RunConfig in the [adk web server](https://github.com/google/adk-python/blob/d327538724f505480c9f764c61d59eee0da92b5c/src/google/adk/cli/adk_web_server.py#L1375-L1399).

It would be nice to have a way to customize max_llm_calls when using and deploying through ADK web. The simplest thing to do would be to add a new field to get_fast_api_app; more robust solutions might be:
- Add new optional field to run methods, which can be surfaced through the Dev UI/by the user on a case by case basis
- Implement something like https://github.com/google/adk-python/issues/1167