api-types: add namespace to BackupGroup

Make it easier by adding an helper accepting either group or
directory

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

pbs-datastore/examples/ls-snapshots.rs

@@ -12,7 +12,7 @@ fn run() -> Result<(), Error> {
 
     let store = unsafe { DataStore::open_path("", &base, None)? };
 
-    for group in store.iter_backup_groups()? {
+    for group in store.iter_backup_groups(Default::default())? {
         let group = group?;
         println!("found group {}", group);