Upgrade to Django to 5.2

[mattiagiupponi]

New Django LTS is 5.2 as reported by the official download page and from the following image

Since the support will end by 2028, it can be worth to upgrade GeoNode to 5.2 with the new GeoNode 5 incoming release.

Release notes are here https://docs.djangoproject.com/en/5.2/releases/5.2/

[giohappy]

The deprecation of the PickleSerializer is a good opportunity to change the way service handlers are serialized and stored in the session.

This is a pretty brittle and hacky solution to avoid requesting the remote capabilities multiple times during the configuration and the harvesting of the remote service.

I suggest disabling the serialization and opening a task to implement a cache for the heavy responses (like the GetCapabilities document)