feat: create public MQTT API for users

[getlarge]

Events are only propagated across microservices at the moment.
It could be great to provide an example implementation of an MQTT ( and Websocket ) API for users and use it in the front end to refresh state in real time without polling.

• Enabling MQTT in RabbitMQ
• Enabling external authentication plugins (HTTP + cache) in RabbitMQ config
• Create NestJS service to interact with RabbitMQ queues over (REST) API (to limit number of queues / user)
• Create authentication endpoints and service in auth service
• Define MQTT topic pattern ( users/${user_id}/${resource}/${action} or reusing Zanzibar notation ? ) and payload schema
• Trigger MQTT events via a new service subscribing to all existing events ? could this facilitate event sourcing ?