RQ: reuse same names as before for Docker entrypoints

[rauchy]

Now that we no longer have Celery around, let's see if we can have the same Docker entrypoints (i.e. functions of the docker_entrypoint script) as before to make upgrades simpler for people.

The only one I'm not sure about is scheduler.

[rauchy]

Before we migrated to RQ, we used to have 3 relevant entry points:

worker, dev_worker and scheduler. We still have all of those, but after migration we have dev_scheduler as well, which does the same as scheduler but with code reloads.

The celery_healthcheck function is no longer relevant, as our Supervisor setup runs healthcheck automatically. How about we just add a deprecation message?

[arikfr]

Previously you could use scheduler to handle the default queue. But that's no more.

Maybe we should use Supervisor to execute two processes when running scheduler in "compatibility" mode? (one for processing jobs and one for scheduler)