Resolve Celery TaskObject Race Condition

[ozer550]

Summary

Description of the change(s) you made

• Added CustomTaskMetadata model to track metadata related to celery TaskResult objects.
• Decouple the relationship between Celery's TaskResult Object and our custom metadata like signature, user_id, channel_id, and progress.
• Create migrations to drop those fields from Celery's TaskResult object and migrate them to CustomTaskMetadata.
• Refactor tests according to new changes.

Manual verification steps performed

1. Ran all the tests.

Does this introduce any tech-debt items?

The only thing that comes to mind is find_incomplete_ids function being executed before the celery TaskObject is saved to the backend asynchronously. This edge case is very difficult to happen relatively as there should surely be some latency due to request, which would ensure the saving of the celery TaskObject in the backend safely. Just to give out some figures the test test_revoke_task when not having a delay between enqueuing and revoking the same tasks creates the above-mentioned issue but if we add a delay of just 0.5 seconds this edge case is not caused.

References

closes #4222

Comments

• The existing tests fairly cover almost all the necessary cases but If there are any more that seem to be necessary to add, would love to add them!

Contributor's Checklist

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• If any Python requirements have changed, the updated requirements.txt files also included in this PR
• Opportunities for using Google Analytics here are noted
• Migrations are safe for a large db

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• Code is clean and well-commented
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Reviewer's Checklist

This section is for reviewers to fill out.

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

WIP

[bjester]

Could be worth checking if our own code calls this, as I overrode on TaskResult to add in the additional fields.

[bjester]

Edited my previous comment: missing the word 'code'. @ozer550 did you check to see if this was used at all? This was used internally to django-celery-results, and overriding it allowed us to add our custom fields to the dict.

[bjester]

Some important notes on the CeleryAsyncResult properties (if they're actually being used still)