Add the ability to set or redefine attributes for messages in Rabbit.

[pmikle]

One of content_type, content_encoding, message_id, user_id, app_id, delivery_mode, priority, timestamp, expiration, type or reply_to, headers.

[pmikle]

Hello, @Seldaek !
I suggest making edits that allow you to set and redefine headers for RabbitMQ queue messages.
I needed to add ttl to messages and I didn't find a way to do it.
Please pay attention to this.
Thank you.

[Seldaek]

Thanks