api2/tape/changer: add drive state to changer status output

if we can find the drive in the config and it has a state

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

src/api2/types/tape/changer.rs

@@ -129,4 +129,7 @@ pub struct MtxStatusEntry {
     /// The slot the drive was loaded from
     #[serde(skip_serializing_if="Option::is_none")]
     pub loaded_slot: Option<u64>,
+    /// The current state of the drive
+    #[serde(skip_serializing_if="Option::is_none")]
+    pub state: Option<String>,
 }