This is similar to the work in bug 1268665. It is /slightly/ more complicated because we have 8 worker processes and each one needs to start with a separate command line argument. But you can do things like this in systemd as you can with supervisor.
https://hg.mozilla.org/hgcustom/version-control-tools/rev/1232a06a77dd3dc60d3623096c5b5893e2160e9a ansible/hg-web: add a systemd service for vcsreplicator (bug 1268722)
https://hg.mozilla.org/hgcustom/version-control-tools/rev/66cf52cdea52787b7192f60c17c4f84702a1a44d ansible/hg-web: finish converting vcsreplicator to a systemd service (bug 1268722)
https://hg.mozilla.org/hgcustom/version-control-tools/rev/b96e6899f07158e7b6307c1b30cbb8321c980c6c vcsreplicator: don't prefix consumer output with time and pid (bug 1268722)
https://hg.mozilla.org/hgcustom/version-control-tools/rev/f3148a57c62ea91c3db00fdb546364a68dad43f5 ansible/hg-web: forward vcsreplicator logs to syslog (bug 1268722)
I'm going to call this one done. supervisor has been uninstalled from all hg.mozilla.org servers. All services are now using systemd. There are still some crons to convert to systemd timers, however.