Add Celery workers to the stack

[pziemkowski]

Description

Following our plan to simplify the stack and allow deployment to VPS, thus limiting hard dependency on AWS I suggest we add Celery workers to handle asynchronous tasks.

In the future we should migrate all asynchronous jobs from Serverless Framework to Celery.
We'll keep Serverless Framework in the stack anyway, because it's still a useful tool for teams developing products in AWS but Celery should be the default task queue.

Describe the solution you'd like

Add Celery configuration to Django project.

Add infrastructure code to deploy Celery to AWS ECS based on the backend docker image.

Add Celery beat service.

Add a single default queue service.

Configure Celery workers on local machine.

Describe alternatives you've considered

No response

Additional context

No response

Validations

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