Add celery-redbeat instead of two separate celery containers

[davinotdavid]

What changed?

• Added celery-redbeat to requirements.txt
• Removed the celery-beat container from docker-compose.yml
• Adjusted the entry.sh file to run with a --beat argument and updated the celery_app to have beat_scheduler as redbeat.RedBeatScheduler

Why?

Infrastructure-wise, it wouldn't be great to have two separate containers for celery and celery without celery-redbeat have concurrency issues when scaling.

How to test

Run the following:

• docker compose down -v
• docker compose up -d --build

Check the celery-worker docker container logs and see the pre-existing tasks registered and the heartbeat running successfully.

Applicable Issues

Fixes #1648

[ryanjjung]

It all checks out! Thanks!