Improve Help Desk standard replies

This was originally proposed on #17935 (comment 160485).

1. Move existing standard replies ("templates") to a place where people who are not Help Desk members can propose improvements → https://gitlab.tails.boum.org/tails/help-desk-shared/-/wikis/templates
2. Help Desk start using this standard reply, we get used to improving & updating it.
3. Write new standard replies as needed, for situations not covered by the existing ones.
   • "This is not Tails specific, we have limited resources, you'll find the answer yourself using your favorite search engine" (some users clearly ask Help Desk before they search the web)
   • "We're aware of this problem, we're working on it, see $ISSUE"
4. Triage the existing standard replies
5. Move the most common/relevant standard replies to our website
   • Done: https://tails.boum.org/support/help_desk_standard_replies/
6. Teach numbat how to propose changes to templates hosted on our website i.e. how to do a MR, presumably via the GitLab web interface → cancelled
7. Decide whether it's worth automating the process of sending this standard reply
   • If it is, see you on #17935 (closed).
8. @sdibella has a look at the content and improves it

Also see https://tails.boum.org/blueprint/Helpdesk_Auto-reply/.