feature: add --factory param

[Sehat1137]

import os

from faststream import FastStream
from faststream.rabbit import RabbitBroker
from faststream.security import SASLPlaintext


def get_app() -> FastStream:
    broker = RabbitBroker(
        host=os.environ["RABBITMQ_HOST"],
        port=int(os.environ["RABBITMQ_PORT"]),
        security=SASLPlaintext(
            username=os.environ["RABBITMQ_USER"],
            password=os.environ["RABBITMQ_PASS"],
        ),
        virtualhost="/",
    )
    faststream = FastStream(broker)
    return faststream

Right now u can start this app like factory

faststream run main:get_app --factory

It`s also support for docs

faststream docs serve main:get_app --factory
faststream docs gen main:get_app --factory

and publish

faststream publish some:get_app --factory --message={}