config: add JobState helper

this is intended to be a generic helper to (de)serialize job states
(e.g., sync, verify, and so on)

writes a json file into '/var/lib/proxmox-backup/jobstates/TYPE-ID.json'

the api creates the directory with the correct permissions, like
the rrd directory

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

src/config.rs

@@ -18,6 +18,7 @@ use crate::buildcfg;
 pub mod acl;
 pub mod cached_user_info;
 pub mod datastore;
+pub mod jobstate;
 pub mod network;
 pub mod remote;
 pub mod sync;