Add the "cc" addresses of an email to the observers of the ticket

[marien-probesys]

Problem

Customers often answers by email by adding other users in copy (i.e. the CC email field). In this case, we would like to add the emails to the observers so they get the future answers.

Solution

Add the "cc" addresses to the list of observers of the ticket.
It may have security consequences though, so we shouldn't design the solution too fast.