fix: Handle email attachments correctly

When the tickets were created from emails asynchronously, the
`createdBy` attribute wasn't set to the message document.
The database refused with a "cannot be null" error.

It worked when collecting emails manually from the interface because the
user was connected.

src/MessageHandler/CreateTicketsFromMailboxEmailsHandler.php

@@ -158,6 +158,7 @@ public function __invoke(CreateTicketsFromMailboxEmails $message): void
                 }
 
                 $messageDocument->setMessage($message);
+                $messageDocument->setCreatedBy($requester);
                 $this->messageDocumentRepository->save($messageDocument, true);
             }