MEMO-781: Create placeholders in the correct order

When the placeholder for an thumbnail, which is at a subpath
[INSTANTIATION_ID]/derived is created before the placeholder for the
instantiation itself, this leads to errors during the ingest, because
fedora creates a pairtree node for each part in a path. Pairtree nodes
can't hold metadata themselves.

src/main/kotlin/RdfHandler.kt

@@ -57,7 +57,7 @@ class RdfHandler(data: String, private val externalBaseUrl: String) {
             statement.getObject().asResource().uri
         }.filterKeep { uri ->
             isInternalNonBinaryResource(uri)
-        }.toList().distinct()
+        }.toList().distinct().sorted()
     }
 
     fun getInstantiations(): List<Pair<String, Model>> {