Add protected storage and documentate sendfile view sample

[sveetch]

Is your feature request related to a problem? Please describe.

Sendfile is available and pre configured in composition repository, however there is not any usage sample.

Describe the solution you'd like

There should be a dedicated storage class for protected medias and an usage sample should be documentated to ease implementation of protected media download (as we did in icon and us).

Additional context

Since v4.2, Django implement a new settings to define all storage, it would be a nice thing to directly use instead of the old way, however it needs to upgrade Bireli from Django 4.1 to 4.2, it should be difficult but we have to ensure everything else is compatible (especially the DjangoCMS stack).

[sveetch]

Django 4.2 support in DjangoCMS is ok since its version 3.11.2.

[sveetch]

Depend on #41