api: namespace management endpoints

allow to list any namespace with privileges on it and allow to create
and delete namespaces if the user has modify permissions on the parent
namespace.

Creation is only allowed if the parent NS already exists.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

pbs-config/src/acl.rs

@@ -85,6 +85,9 @@ pub fn check_acl_path(path: &str) -> Result<(), Error> {
             if components_len <= 2 {
                 return Ok(());
             }
+            if components_len > 2 && components_len <= 2 + pbs_api_types::MAX_NAMESPACE_DEPTH {
+                return Ok(());
+            }
         }
         "remote" => {
             // /remote/{remote}/{store}