Handling of celery workers in list of workers

In the list of workers, you get to see the "Celery" worker:

It is marked as "Never seen" and as "Disabled". The disabled flag is clearly wrong, because the worker is processing server tasks. However that worker has no associated token and this likely explains why that value is shown. The never seen also makes no sense since that worker is the most reliable and is always available.

I suggest that we entirely hide the celery worker from that list. We care about "external" workers" (normal and signing) mainly in that view, i.e. are they connected and are they idle or busy?

The celery worker can't accurately be represented since it processes multiple work requests in parallel contrary to the other external workers.