Bug 26363: Provide a systemd unit file for koha-worker for source installs

This patch adds a systemd unit file which gets rewritten according to
the configuration specified by Makefile.PL. This can be linked or
copied to systemd directories for running a systemd service for
background_jobs_worker.pl

Test plan:
1. perl Makefile.PL
1a. Choose "single" installation
1b. Choose "/opt/koha" for a file path
2. make
3. vi blib/KOHA_CONF_DIR/koha-worker.service
4. Verify that PERL5LIB, KOHA_CONF, ExecStart, and SyslogIdentifier
all appear to be correctly filled in

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 21a850a3dc)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>

Makefile.PL

@@ -673,6 +673,7 @@ my $pl_files = {
          'blib/KOHA_CONF_DIR/koha-conf.xml',
          'blib/KOHA_CONF_DIR/koha-httpd.conf',
          'blib/KOHA_CONF_DIR/log4perl.conf',
+         'blib/KOHA_CONF_DIR/koha-worker.service',
          'blib/ZEBRA_CONF_DIR/etc/default.idx',
          'blib/MISC_DIR/koha-install-log'
          ],

etc/koha-worker.service

@@ -0,0 +1,17 @@
+# koha-worker.service
+[Unit]
+Description=Koha Task Queue Worker
+After=syslog.target network.target
+
+[Service]
+Environment=PERL5LIB=__PERL_MODULE_DIR__
+Environment=KOHA_CONF=__KOHA_CONF_DIR__/koha-conf.xml
+ExecStart=__SCRIPT_DIR__/background_jobs_worker.pl
+Restart=on-failure
+RestartSec=5s
+StartLimitBurst=3
+StartLimitInterval=60
+SyslogIdentifier=koha-worker-__DB_NAME__
+
+[Install]
+WantedBy=multi-user.target