restore: complete the latest full backup task of site id

when creating a full backup, the task is still running and the database
dump which is part of the backup, still says it is still running.

during restore, we mark the taskId as completed. detection of the task
is using the siteId in config (when restoring via backup config) or
just blindly setting the last backup task as completed (in manual form fill).

dashboard/src/components/app/Backups.vue

@@ -229,6 +229,8 @@ async function onDownloadConfig(backup) {
     tmp[k] = backupSite[k];
   }
 
+  tmp.siteId = backupSite.id;
+
   const filename = `${props.app.fqdn}-backup-config-${(new Date(backup.creationTime)).toISOString().split('T')[0]}.json`;
   download(filename, JSON.stringify(tmp, null, 4));
 }