Bug 31469: log4perl.conf: Add %n to conversionpattern for Plack

Bug 31469: log4perl.conf: Add %n to conversionpattern for Plack

The PLACKOPAC, PLACKAPI and PLACKINTRANET appenders still need %n
(i.e. a newline). Note that this patch does not add %l since it
is a bit confusing because it adds a lot of Plack internal noise like:
    [2022/09/29 08:51:34] [WARN] Test mainpage CGI::Compile::ROOT::usr_share_koha_mainpage_2epl::__ANON__ /usr/share/koha/mainpage.pl (49)

The patch is a result of:
    git grep -l "log4perl.appender.PLACK" | xargs sed -i -e"/ConversionPattern/ s/%m$/%m%n/"

Test plan:
First run: sed -i -e"/ConversionPattern/ s/%m$/%m%n/" /etc/koha/sites/[YOUR_CLONE]/log4perl.conf
Edit that file, change PLACKOPAC to debug level like:
    log4perl.logger.plack-opac = DEBUG, PLACKOPAC
Restart.
Hit an OPAC page twice.
Check plack-opac logfile and verify that it contains a newline between last two messages like:
    [2022/09/29 08:04:30] [DEBUG] kohaversion : 22.0600054
    [2022/09/29 08:04:42] [DEBUG] kohaversion : 22.0600054

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>