Provide example HTTP and RabbitMQ API implementations

## What's the problem?

Each of our current services follow about the same architecture, and are written in the same language.
They should thus use the same code for their APIs, in order to reduce bugs and implementation efforts.

## What's the solution?

Provide working examples of implementing an HTTP REST CRUD API and RabbitMQ producers/consumers, with documented code.

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Note: This issue is critical for the Beep Hackathon for a smooth experience of service coding, and generally improves service development.