sync/pull: make namespace aware

sync/pull: make namespace aware

Allow pulling all groups from a certain source namespace, and
possibly sub namespaces until max-depth, into a target namespace.

If any sub-namespaces get pulled, they will be mapped relatively from
the source parent namespace to the target parent namespace.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>