[BUGFIX] Add configuration to set SMTP mail domain

If you use some mail relay servers for sending emails via
SMTP, it is necessary to specify the domain name under which
the emails are sent. This is especially important for the Gmail-Relay
server smtp-relay.gmail.com but is not limited to this.

Resolves: #93635
Releases: master
Change-Id: If2fca7d02cc5c8017ae7eebcd616a165c4d9bb1b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/69652


Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Lina Wolf <112@linawolf.de>
Reviewed-by: Guido Schmechel <guido.schmechel@brandung.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>