move worker_task.rs into proxmox-rest-server crate

Also moved pbs-datastore/src/task.rs to pbs-tools, which now depends on 'log'.

pbs-tools/src/lib.rs

@@ -24,6 +24,7 @@ pub mod str;
 pub mod stream;
 pub mod sync;
 pub mod sys;
+pub mod task;
 pub mod ticket;
 pub mod tokio;
 pub mod xattr;