Make "staff", not "superuser" to be sufficient to access embargoed data

[yarikoptic]

ATM we do not really use staff level of access in django and only superuser:

❯ git grep is_staff
dandiapi/api/admin.py:    list_filter = ['metadata__status', 'is_staff', 'is_superuser', 'is_active']
❯ git grep is_super
dandiapi/api/admin.py:    list_filter = ['metadata__status', 'is_staff', 'is_superuser', 'is_active']
dandiapi/api/permissions.py:            request.user.is_superuser
dandiapi/api/permissions.py:                request.user.is_superuser
dandiapi/api/services/dandiset/__init__.py:    if identifier and not user.is_superuser:
dandiapi/api/tests/test_users.py:        'admin': social_account.user.is_superuser,
dandiapi/api/views/auth.py:        and not user.is_superuser
dandiapi/api/views/dashboard.py:        return self.request.user.is_superuser
dandiapi/api/views/dashboard.py:    if not request.user.is_superuser:
dandiapi/api/views/users.py:        'admin': user.is_superuser,
dandiapi/api/views/users.py:        'admin': user.is_superuser,
dandiapi/api/views/users.py:        'admin': user.is_superuser,
dandiapi/api/views/version.py:        if not request.user.is_superuser:

I would feel a bit safe (although would it be just red-herring) if we pretty much allow staff level, not superuser (more destructive) level to access API accessible "secret" (embargoed) data and "dangerous" functionality and leave "superuser" level only for really "core" users/actions? WDYT?