Document expectations for Front-Desk work

as requested in this monthly meeting:
http://meetbot.debian.net/debian-lts/2022/debian-lts.2022-09-22-13.58.html

Front-Desk is currently documented at 2 places:
https://freexian-lts.gitlab.io/lts/information-for-lts-contributors.html#lts-frontdesk-duties (private, short)
https://lts-team.pages.debian.net/wiki/LTS-Development.html#frontdesk-duties (public, detailed)

bits to recap:
buxy> I usually expect that people in charge of FD do CVE triaging on a daily basis on work days at least, is that a shared expectation?
buxy> by work days I mean Monday to Friday, but security issues do not stop during week-ends
buxy> Do we relax rules to bypass FD during WE or do we expect FD to also work during WE?
ta> I would say on urgent issues FD can be bypasswd on the weekend and holidays, but not for normal stuff
Beuc> It's pretty rare that something is so urgent that a day or two matters, usually in such cases (e.g. sudo CVE) somebody feels entitled to take things over, probably one of the people on the private secteam list
apo> buxy: not sure, but we are aware of them anyway because Thorsten and myself get notified
ta> I have never seen an embargo ending on the weekend

• complement existing section about work days and bypass in private doc
• possibly move/link everything to public doc, there's much overlap