Merge pull request #21 from observeinc/alew/rhel

fix: update command to work on debian + rhel in preinstall.sh

Author: obs-gh-alexlew

packaging/linux/scripts/preinstall.sh

@@ -2,7 +2,7 @@
 
 # Set up user and permissions
 getent passwd observe-agent >/dev/null || useradd --system --user-group --no-create-home --shell /sbin/nologin observe-agent
-sudo adduser observe-agent systemd-journal
+sudo usermod -a -G systemd-journal observe-agent
 
 sudo mkdir -p /var/lib/observe-agent/filestorage
 sudo chown observe-agent /var/lib/observe-agent/filestorage