Bug#826297: offer a shutdowm logging service

[積丹尼 Dan Jacobson]

Package: systemd
Version: 230-2
Severity: wishlist

In https://freedesktop.org/wiki/Software/systemd/Debugging/#index2h1
one sees it is quite possible to save a /shutdown-log.txt .

Alas the method there does not work on Debian. No /shutdown-log.txt is
produced.

Please:
1. Make it work on Debian.
2. Offer it as a convenient service that one can just enable / disable.

By the way, it would be great if boot logs could also be kept in such a
fashion too.