Investigate the use of Python Celery for API job queueing

[securestep9]

at the moment, Nettacker is using Python multi-threading for API tasks, which is not very scalable. It would be good to replace it with a proper task queue system that can handle retires/tracking/background jobs and scheduled jobs. Something like RabbitMQ is probably overkill for now, but Celery is an interesting and widely used Python-based task queue that can be used to improve Nettacker