api-types: introduce BackupType enum and Group/Dir api types

The type is a real enum.

All are API types and implement Display and FromStr. The
ordering is the same as it is in pbs-datastore.

Also, they are now flattened into a few structs instead of
being copied manually.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

src/api2/tape/media.rs

@@ -441,7 +441,7 @@ pub fn list_content(
         for (store, snapshot) in media_catalog_snapshot_list(status_path, &media_id)? {
             let backup_dir: BackupDir = snapshot.parse()?;
 
-            if let Some(ref backup_type) = filter.backup_type {
+            if let Some(backup_type) = filter.backup_type {
                 if backup_dir.group().backup_type() != backup_type {
                     continue;
                 }