[Feature Request] populate $SERVICE_NAME or logdir configuration

[RichardKraus]

It would be helpful to make $SERVICE_NAME or similar expand to the service name on service load (if sub-vars is set). This could eliminate the need to retype the logfile name for each service.

alternatively it could also be quite nice to have a logdir option (or handle dirs in logfiles) by creating a logfile <service name>.log in that directory.

If that is already a thing then I did not find it yet.