api2/tape/backup: add 'force-media-set' parameter to manual backup

so that a user can force a new media set, e.g. if he uses the
allocation policy 'continue', but wants to manually start a new
media-set.

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

src/api2/tape/media.rs

@@ -129,7 +129,7 @@ pub async fn list_media(
         // Call start_write_session, so that we show the same status a
         // backup job would see.
         pool.force_media_availability();
-        pool.start_write_session(current_time)?;
+        pool.start_write_session(current_time, false)?;
 
         for media in pool.list_media() {
             let expired = pool.media_is_expired(&media, current_time);