add sparseinit to has_feature

we will use this for determining
if we need to write zeros to a volume

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

PVE/Storage/ZFSPoolPlugin.pm

@@ -577,6 +577,7 @@ sub volume_has_feature {
 	clone => { base => 1},
 	template => { current => 1},
 	copy => { base => 1, current => 1},
+	sparseinit => { base => 1, current => 1},
     };
 
     my ($vtype, $name, $vmid, $basename, $basevmid, $isBase) =