Add RabbitMQ as message queue solution

[svix-gabriel]

Motivation

This adds RabbitMQ as an alternative internal queueing system (instead of in-memory or redis based queueing).

That's pretty much it. The RabbitMQ integration has only been tested locally using E2E tests, so there may be issues that only show up on a larger scale that need addressing. As such, this should be treated as an MVP. Be cautious about using the RabbitMQ solution in a production environment for the time being. The README hasn't been updated yet for precisely this reason.

Solution

All in all, this requires a few changes

• Adding the integration to the local docker-compose testing suite. There's an adjacent rabbit folder for including the delayed message plugin, for, well, sending delayed messages 😃
• Adding the actual queue implementation
• The test that checks multiple concurrent workers was updated to ack messages.