refactor: add CELERY_RESULT_BACKEND with default django-cache

[navinkarkera]

Description

Cherry pick of openedx/openedx-platform#30244

At Opencraft, we want to run multiple instances of celery workers in separate servers. The celery workers need to be able to share task results. Currently, the CELERY_RESULT_BACKEND is hard coded to use django-cache.

So this PR allows to setup CELERY_RESULT_BACKEND via configuration.

To use django ORM as celery backend, one can set CELERY_RESULT_BACKEND to django-db as described in docs.

Supporting information

• Task: https://tasks.opencraft.com/browse/BB-6077

Deadline

"None"

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[natabene]

@navinkarkera Thank you for your contribution, is this ready for our review?

[navinkarkera]

@natabene Thank you! Yes it s ready for your review.
cc: @kaustavb12

[kaustavb12]

👍

Looks good to go from my end.

• I tested this: I tested the configuration in the PR sandbox
• I read through the code
• Includes documentation

[adzuci]

@navinkarkera Would you mind rebasing this PR?

[navinkarkera]

@navinkarkera Would you mind rebasing this PR?

@adzuci It is already up to date with nutmeg branch.

[NIXKnight]

LGTM 👍

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