Add userIdentifier to Symfony Mailer handler

[Chris53897]

If i remember correct the old Swiftmailer handler did include the userIdentifier of the logged in User.

The actual Symfony Mailer handler does not include this info.
https://symfony.com/doc/current/logging/monolog_email.html

This would help the reciever to fix the error. And maybe notify the user.

Or is there a reason that this field is not included?