[Python] Simplify the AgentChat quickstart example

[ekzhu]

• The code example is still a bit complex.

The new code example:

from autogen_agentchat.agents import AssistantAgent
from autogen_agentchat.ui import Console
from autogen_ext.models.openai import OpenAIChatCompletionClient


# Define a tool
async def get_weather(city: str) -> str:
    return f"The weather in {city} is 73 degrees and Sunny."


async def main() -> None:
    # Define an agent
    weather_agent = AssistantAgent(
        name="weather_agent",
        model_client=OpenAIChatCompletionClient(
            model="gpt-4o-2024-08-06",
            # api_key="YOUR_API_KEY",
        ),
        tools=[get_weather],
    )
   # Run a query
   stream = weather_agent.run_stream(task="What's the weather like in Seattle, WA")
   # Display output in console
   await Console(stream)


# NOTE: if running this inside a Python script you'll need to use asyncio.run(main()).
await main()