Add RabbitMQ support

[jose-lopes]

I worked on adding RabbitMQ support as Message Bus. I created an abstraction, so we can choose to use NATS or RabbitMQ based on MESSAGEBUS_URL option.

Please feel free to review and give me your comments. If you want me to change anything, let me know, I will be glad to receive feedback and improve the code.

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This change is