fix(config): attempt to deserialize deep directory structure before flat

This meant that if you had set the directory structure, than it would
always deserialize as "Flat".
We also migrate the newly migrated media to the deep directory structure,
if configured.

src/config/mod.rs

@@ -527,8 +527,8 @@ impl Default for DirectoryStructure {
 #[derive(Deserialize)]
 #[serde(untagged)]
 enum ShadowDirectoryStructure {
-    Flat {},
     Deep { length: NonZeroU8, depth: NonZeroU8 },
+    Flat {},
 }
 
 impl TryFrom<ShadowDirectoryStructure> for DirectoryStructure {