fix: ensure the dokku-retire timer is properly installed

Closes #3615

plugins/scheduler-docker-local/install

@@ -38,9 +38,15 @@ Description=Run dokku-retire.service every 5 minutes
 
 [Timer]
 OnCalendar=*:0/5
+Persistent=true
+
+[Install]
+WantedBy=timers.target
 EOF
     if command -v systemctl &>/dev/null; then
       systemctl --quiet reenable dokku-retire
+      systemctl --quiet enable dokku-retire.timer
+      systemctl --quiet start dokku-retire.timer
     fi
   else
     cat <<EOF >/etc/cron.d/dokku-retire