Import latest code changes from Django 4.0

[jcugat]

Used the current stable version of Django (4.0) as the reference for all the changes.

It includes, among other things:

• EmailUserCreationForm does not strip whitespaces in the password fields, to match Django's behavior.
• EmailUserCreationForm supports custom password validators configured by AUTH_PASSWORD_VALIDATORS.
• EmailUser.objects.create_superuser() allows empty passwords. It will also check that both is_staff and is_superuser parameters are True (if passed). Otherwise, it would create an invalid superuser.