Subscriber iterator for rabbit mq

[ApostolFet]

Description

Asynchronous generator over aio-pika iterator to implement an iterator for rabbit mq subscriber

Fixes #1881

Type of change

• New feature (a non-breaking change that adds functionality)
• This change requires a documentation update

Checklist

• My code adheres to the style guidelines of this project (scripts/lint.sh shows no errors)
• I have conducted a self-review of my own code
• I have made the necessary changes to the documentation
• My changes do not generate any new warnings
• I have added tests to validate the effectiveness of my fix or the functionality of my new feature
• Both new and existing unit tests pass successfully on my local environment by running scripts/test-cov.sh
• I have ensured that static analysis tests are passing by running scripts/static-analysis.sh
• I have included code examples to illustrate the modifications

[Lancetnik]

process_message return None if only the original message is None.

So, we should return RabbitMessage everytime

[Lancetnik]

Please, add __aiter__ method to the SubscriberProto parent as well