feat: support asgi frameworks directly in asgi mode

[taeold]

This PR enables the Functions Framework to automatically detect and run ASGI web frameworks like FastAPI and Starlette. When the framework detects an ASGI app, functions framework handles the set up without requiring any special configuration.

This allows developers to easily deploy modern Python web frameworks with their full feature set (routing, middleware, validation) to Cloud Run functions.

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello World"}

@app.get("/items/{item_id}")
def read_item(item_id: int):
    return {"item_id": item_id}

Load the app in functions framework:

functions-framework --target app --asgi

[maemayve]

Seems to me that this is offering a path for deploying python code that doesn't conform with the Functions API definition. I think we need to review with the product specification to determine if this is an approach that works with the intent of the framework