Update for django 4

[jcohen02]

Django 4 removes django.conf.urls.url which was being used in the django-drf-filepond URL mappings.

This needs to be fixed by moving to django.urls.path or re_path. However, switching to these will remove compatibility with Python 2.7. Since Python 2.7 support is not yet officially deprecated, this should be done in v0.5.0 with a view to that being the last version providing py2.7 support.

This was fixed in #66 with python 2.7 support re-introduced with the updates in #67.