Have a footer on tails-bugs@ inviting to donate

Frontdesk is an important part of our expenses and people receiving personalized help from us might be more willing to donate. We could add a footer pointing to the donation page at the bottom of the emails sent by tails-bugs@ (that’s possible in Schleuder).

If people don’t like our support or are pissed of at us, they would only get a bit more pissed off and that won’t change much anyway :)

Parent Task: #9855 (closed)

Original created by @sajolida on 11726 (Redmine)