Bug 33964: Use Email::Sender::Transport::SMTP::Persistent for sending email

Bug 33964: Use Email::Sender::Transport::SMTP::Persistent for sending email

As described in bug 30013, some outgoing SMTP services ( such as Gmail ) do not like Koha's current behavior of initiating a new connection for each email sent.  If we switch from Email::Sender::Transport::SMTP to Email::Sender::Transport::SMTP::Persistent and store the object for the duration of the message queue processing, this should solve that issue.

Signed-off-by: Sam Lau <samalau@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>