[DURACOM-412] Update findByCustomURL return code documentation.

Change return code from 204 No content to 404 Not found when no item is found with the given custom URL, reflecting the actual implementation.

Author: AdamF42

items.md

@@ -614,5 +614,5 @@ Search an item by the provided custom url. If the provided url is an UUID, a fin
 
 Return codes:
 * 200 OK - if the operation succeed
-* 204 No content - if the operation succeed but no item was found
+* 404 Not found - if no item was found with the given custom URL
 * 500 Internal server error - if multiple item was found related to the given url