Added the CELERY_RESULT_EXTENDED setting and set to True

[vanbuiten]

Description

The CELERY_RESULT_EXTENDED setting is added and set to True. This will add the missing information to the database. This is a known issue in release 2.4.0 see celery/django-celery-results#326

Checklist

• Keep the PR, and the amount of commits to a minimum
• The commit messages are meaningful and descriptive
• The change/fix is well documented, particularly in hard-to-understand areas of the code / unit tests
• Check that the branch is based on master and is up to date with master
• Check that the PR targets master
• There are no merge conflicts and no conflicting Django migrations

How has this been tested?

• Tested the change/fix locally and all unit tests still pass
• Code coverage is at least 85% (the higher the better)
• No iSort, Flake8 and SPDX issues are present in the code

[tcoenen]

Akkoord!