feat: start celery worker programmatically (#2988)

### Description

Allow us to be more flexible with the option passed the celery worker,
for example, to change the logging level.

Dockerfile

@@ -201,14 +201,7 @@ RUN --mount=type=cache,target=/root/.cache/pip \
 USER ${UID}:${GID}
 WORKDIR /app
 
-CMD ["/usr/local/bin/celery", "worker", \
-    "--app=libretime_worker.tasks:worker", \
-    "--config=libretime_worker.config", \
-    "--beat", \
-    "--time-limit=1800", \
-    "--concurrency=1", \
-    "--loglevel=info"]
-
+CMD ["/usr/local/bin/libretime-worker"]
 ARG LIBRETIME_VERSION
 ENV LIBRETIME_VERSION=$LIBRETIME_VERSION