api2: add status/datastore-usages api call

returns a list of the datastores and their usages, a list of usages of
the past month (for the gui) and an estimation of when its full
(using the linear regression)

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

src/api2.rs

@@ -24,6 +24,7 @@ pub const SUBDIRS: SubdirMap = &[
     ("nodes", &NODES_ROUTER),
     ("pull", &pull::ROUTER),
     ("reader", &reader::ROUTER),
+    ("status", &status::ROUTER),
     ("subscription", &subscription::ROUTER),
     ("version", &version::ROUTER),
 ];