Feature:Support MultiProcess Collector for PrometheusMiddleWare

[C3EQUALZz]

I encountered a problem that if MultiProcessCollector from prometheus_client is used, then the metrics are simply not collected. Only #TYPE and #HELP appear. I learned from one of the contributers - Roman Frolov - of FastStream that this functionality is missing, he asked me to create a Issue to add this functionality.

It would be cool if you add a flag for Middleware multiprocess=True or something like that.

from typing import Final
from faststream import FastStream
from faststream.kafka import KafkaBroker
from app.settings import Settings, get_settings()

settings: Final[Settings] = get_settings()
registry: Final[CollectorRegistry] = CollectorRegistry()
multiprocess.MultiProcessCollector(registry, path=settings.project_dir / settings.server.multiprocess_dir)

broker: KafkaBroker = KafkaBroker(
            settings.broker.url,
            middlewares=[
                KafkaPrometheusMiddleware(
                    registry=registry,
                    app_name="faststream-some-service",
                    multiprocess=True
                ),
            ]
        )

Environment
Running FastStream 0.5.40 with CPython 3.12 on Windows