Upgrade django 

We're currently using [django 3.1.5](https://github.com/opencleveland/refundcleveland/blob/93573ebf59ab8e267d1926bdc65db7902c5b3398/requirements.txt#L4) which is deprecated and not receiving anymore security updates (ref: 
https://www.djangoproject.com/download/

Determine whether it's worth upgrading to 4.0, 5.Z or just update to 3.2 which will be supported through 2024. 