[Docker] Rewrite entrypoint

This adds a minimal init process so we get clean signal processing. It also removes anything from the entrypoint except startup of AlekSIS with runuwsgi, as this can now start celery alongside the web handler if so desired.

aleksis/core/settings.py

@@ -533,7 +533,7 @@ CELERY_BEAT_SCHEDULER = "django_celery_beat.schedulers:DatabaseScheduler"
 if _settings.get("celery.email", False):
     EMAIL_BACKEND = "djcelery_email.backends.CeleryEmailBackend"
 
-if _settings.get("dev.uwsgi.celery", True):
+if _settings.get("dev.uwsgi.celery", DEBUG):
     concurrency = _settings.get("celery.uwsgi.concurrency", 2)
     UWSGI.setdefault("attach-daemon", [])
     UWSGI["attach-daemon"].append(f"celery -A aleksis.core worker --concurrency={concurrency}")