limit username length

src/ez_lan_manager/services/UserService.py

@@ -12,6 +12,7 @@ class NameNotAllowedError(Exception):
 
 class UserService:
     ALLOWED_USER_NAME_SYMBOLS = ascii_letters + digits + "!#$%&*+,-./:;<=>?[]^_{|}~"
+    MAX_USERNAME_LENGTH = 14
 
     def __init__(self, db_service: DatabaseService) -> None:
         self._db_service = db_service