Fix celery healthcheck memory leak

There was a strange bug where over a few months, celery's
idle CPU usage kept increasing. It seems this may have been related
to the healthcheck being killed by docker, without cleaning up after
itself. This lead to hundreds of thousands of 'celery.pidbox' keys
being left behind on redis, which slowed down redis.

See celery/celery#6089

infra/concrexit/worker-entrypoint.sh

@@ -13,6 +13,8 @@ done
 
 exec runuser -u appuser -- celery --app thaliawebsite worker \
     --loglevel INFO \
-    --concurrency 4 \
+    --concurrency 2 \
+    --without-gossip \
+    --heartbeat-interval 10 \
     --beat \
     --schedule /volumes/worker/celery-beat-schedule

infra/docker-compose.yml

@@ -41,9 +41,9 @@ services:
     restart: always
     healthcheck:
       test: [ "CMD", "pg_isready", "--username", "concrexit" ]
-      interval: 2s
-      timeout: 2s
-      retries: 30
+      interval: 10s
+      timeout: 5s
+      retries: 5
 
   redis:
     image: redis:7.2-alpine
@@ -53,9 +53,9 @@ services:
     restart: always
     healthcheck:
       test: [ "CMD-SHELL", "redis-cli ping | grep PONG" ]
-      interval: 2s
-      timeout: 2s
-      retries: 10
+      interval: 10s
+      timeout: 5s
+      retries: 5
 
   worker:
     image: ghcr.io/svthalia/concrexit:${TAG:-development}
@@ -75,10 +75,12 @@ services:
       concrexit:
         condition: service_started
     healthcheck:
-      test: [ "CMD", "celery", "--app", "thaliawebsite", "status" ]
-      interval: 10s
-      timeout: 3s
-      retries: 10
+      # The celery status timeout needs to be smaller than docker's timeout.
+      # Otherwise, celery will fail to clean up after itself on redis.
+      test: [ "CMD", "celery", "--app", "thaliawebsite", "status", "--timeout=5" ]
+      interval: 30s
+      timeout: 10s
+      retries: 5
 
 volumes:
   concrexit-media: