Allow CC'ing incoming_email and service_desk_email
Release notes
It may happen that throughout communication by mail between a service desk and the person contacting the service desk, the service desk may not be addressed through the "To" header but instead get a mail via "CC". Naively, I would expect this to work as it does with other ticket systems - either generating a new issue or (how?) put the next "communication item" inside the corresponding service desk issue.
Problem to solve
CC'ing a service desk should be interpreted by GitLab and produce an issue inside a (the corresponding) repositories service desk. At the moment the mail does get into the central inbox where Gitlab cannot find the correct service desk as the "To" header is reaching out to another address - probably unknown. I don't see any reason why this should not be "stackable" in the sense that multiple service desks could be mentioned in "To" and "CC".
Intended users
Everyone using the Service Desk feature.
Reference
This issue was created after communication in ticket/request #255640