syncjob: change worker type for sync jobs

'sync' is used for manually pulling a remote datastore
changing it for a scheduled sync to 'syncjob' so that we can
differentiate between both types of syncs

this also adds a seperate task description for it

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

src/bin/proxmox-backup-proxy.rs

@@ -510,7 +510,7 @@ async fn schedule_datastore_sync_jobs() {
             }
         };
 
-        let worker_type = "sync";
+        let worker_type = "syncjob";
 
         let last = match lookup_last_worker(worker_type, &job_id) {
             Ok(Some(upid)) => {