This is NixOS' recommended way to setup service dirs
https://github.com/NixOS/nixpkgs/pull/56265. This commit hands off the
initial data directory creation to systemd.tmpfiles.rules. All other
preStart scripts are left intact to limit this changes' scope.
This better fits the semantics of this unit and allows for easier
automated testing whether the service is active.
wantedBy = bindsTo = after = tor.service is the simplest way to ensure
that this unit is always running/restarted in lockstep with tor.
Previously, onion-chef would have stayed inactive in the case
that tor was stopped and then later restarted.
