Bug#1023596: bookworm: document changes in default rsyslog configuration

[Richard Lewis]

Makes sense.

Just wanted to add a link to the related logcheck bug which just got
filed: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1023755
- even if this gets fixed in logcheck, users of rsyslog need to make
the same change to all locally-written logcheck rules (and there are
probably some installed by other packages) so impact is still worth
documenting in release-notes imo