Feature: need in receiving headers of certain kafka messages in batch subscription mode about faststream

[Lancetnik]

We are working on it as a part of #1398 (#916) wait a bit for release

But, if you want to make it manually, you can access to all messages' headers from the raw_messages (list of ConsumerRecords)

from faststream.kafka import KafkaMessage

@broker.subscruber("in", batch=True)
async def handler(..., message: KafkaMessage):
     for msg in message.raw_message:
         print(msg.headers)  # unserialized kafka headers