[pve-devel] allow ldap group access

[Dietmar Maurer]

> mhm but then we still need to manually sync deleted or added users.
> Great would be to give a group of ldap users access. 

No, that would not be great. This would result in many LDAP queries each time
you need to check permissions, or when you need a list of users.

Instead, we need to cache the list of valid users, and that cache is called users.cfg.