Add email notification service

[pl-buiquang]

• [ ] a new email field should be added to the user model (can be fetch using the ldap connector)
• [ ] a email notification service should be added allowing to send templated messages to user or predefined address (support)
• [ ] use email notification option when launching a study (sending email when the result is ready)
• [ ] add email backend to the help form (#470)

This concerns a certain number of events whose processing takes quite a long time and would require notification. For example, launch, ZIP export, copy of a study...

[laurent-laporte-pro]

See internal documentation Relais SMTP dédié aux applications Back-Office