Replace unmaintained django-cas-client by django-cas-ng

[Badatos]

As django-cas-client (https://github.com/kstateome/django-cas) hasn't been updated since 2019, this PR replace it by more up-to-date django-cas-ng (https://github.com/django-cas-ng/django-cas-ng) (last updated last month)

• Replace "get" method in logout by "post" ("get" will be deprecated in django 5.x)
• Add pod_affiliation_handler() func to set staff status to CAS users with AFFILIATION in AFFILIATION_STAFF
• Replace CAS_RESPONSE_CALLBACKS by `cas_user_authenticated_callback
• Check auto group creation from affiliations

[gitguardian]

️✅ There are no secrets present in this pull request anymore.

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