Fix memory usage on Celery worker

[Uxio0]

What is needed?

Fix memory usage on Celery worker

Background

• Celery worker is steadily increasing the used RAM until it's restarted
• It makes us think it's a memory leak: Continuous memory leak celery/celery#4843

Solution

Setting worker reboot after a number of tasks or after ram is used:

• https://docs.celeryproject.org/en/stable/userguide/configuration.html#std-setting-worker_max_tasks_per_child
• https://docs.celeryproject.org/en/stable/userguide/configuration.html#worker-max-memory-per-child

[Uxio0]

It's currently not supported for gevent, only prefork: https://docs.celeryproject.org/en/stable/userguide/workers.html#max-tasks-per-child-setting

[Uxio0]

Maybe max_memory_per_child works, there's no warning or error when running Celery with that flag