[Feature request]Support configureble chat_model

[moritalous]

It would be more versatile and better if we could set chat_model as configurable so that we could freely change chat_model-specific parameters (such as extended shinking in Claude 3.7 Sonnet or reasoning_effort in o3-mini). What do you think?

For example:

thread = {"configurable": {"thread_id": str(uuid.uuid4()),
 "search_api": "tavily",
 "planner_chat_model": ChatOpenAI(model="o3-mini"),
 "writer_chat_model": ChatAnthropic(model="claude-3-7-sonnet-latest",  thinking={"type": "enabled", "budget_tokens": 16_000}),
 "report_structure": REPORT_STRUCTURE,
 "max_search_depth": 1,}
 }

The default behavior is as it is now, and I think it would be good to prepare it as an advanced setting.