pbs-config: acl-tree: add any_priv_below

pbs-config: acl-tree: add any_priv_below

`any_priv_below()` checks if a given AuthId has any given privileges
on a sub-tree of the AclTree. to do so, it first takes into account
propagating privileges on the path itself and then uses a depth-first
search to check if any of the provided privileges are set on any
node of the sub-tree pointed to by the path.

Signed-off-by: Stefan Sterz <s.sterz@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>