Set default_auto_field to BigAutoField and fix migrations

See merge request !596

Resolve "Drop Python <3.9 compatibility"

Closes #420

See merge request !594

Rationale: We drop Python <3.9 support

Rationale: We drop support for Python <3.9

Update poetry.lock

See merge request !597

Protect celery-progress endpoint

Closes #379

See merge request !595

Resolve "Correctly implement the ckeditor"

Closes #340

See merge request !585

Resolve "PDF is rendered without request in context"

Closes #430

See merge request !588

Resolve "Make django-cachalot compatible with Django 3.2"

Closes #426

See merge request !587

Merge branch '432-synchronisation-between-aleksis-and-django-groups-works-incompletely' into 'master'

Resolve "Synchronisation between AlekSIS and Django groups works incompletely"

Closes #432

See merge request !590

Merge branch '404-remove-old-data-check-results-if-the-data-problem-persists-no-longer' into 'master'

Resolve "Remove old data check results if the data problem persists no longer"

Closes #404

See merge request AlekSIS/official/AlekSIS-Core!580

Enable the Django REST framework

See merge request !586

Resolve "Serve as OAuth2 and OpenID Connect provider"

Closes #235

See merge request !415

Merge branch '235-serve-as-saml-and-oauth2-provider' of edugit.org:AlekSIS/official/AlekSIS-Core into 235-serve-as-saml-and-oauth2-provider