Hot-reload support to celery

[yotamtal]

Description

This PR adds support for celery hot-reloading while developing, on changes to tasks.py and celery_app.py files when setting up a project with docker and celery.

Rationale

I have been using this Cookiecutter template for many projects and while developing with celery tasks I had to restart the worker manually to test the changes. This minor change will allow developers to test their celery tasks faster

Use case(s) / visualization(s)

-> Develop celery tasks -> notice a bug -> change the code -> save -> test the new code without restarting the worker manually

[foarsitter]

Nice addition!

Is the pattern not to tight? Now the restarts do not happen when there are changes made to settings.py or models.py. So why not set it to *.py?

[yotamtal]

@foarsitter I configured it that way on purpose, since I write all my tasks in those files.
I tried setting it as *.py before and then it restarts the worker on every save and the hot reload takes more time and mess up the logs, so I think this is the most efficient way to go :)

[browniebroke]

Nice addition indeed. Good question for the pattern, I'm not sure I understand the problem, but I probably just need to try it out 😄

[pySilver]

Nice work! Consider using watchgod instead of watchdog. Watchgod is used by uvicorn as an optional changes watcher, so it would solve both cases at the same time! :)

[scnerd]

This is a great feature idea. Is there anything still needed before this can be merged (besides simply resolving the merge conflicts)?

[browniebroke]

Yes, I kind of forgot about it, I think it's good to go.

[browniebroke]

Thanks for your contribution @yotamtal 🎉