use journal namespace

config/journald/journald@terraria.conf

@@ -0,0 +1,11 @@
+# Settings for the Terraria servers' own journal (LogNamespace=terraria).
+# Read it with:  journalctl --namespace=terraria -u terraria@<name>
+# After changing this file:  sudo systemctl restart systemd-journald@terraria
+# All options: man journald.conf
+
+[Journal]
+# Disk space the servers' logs may use, kept separate from the system journal
+SystemMaxUse=256M
+RuntimeMaxUse=64M
+# Uncomment to delete entries older than this
+#MaxRetentionSec=3month