[Nut-upsuser] On retiring some terminology

[Roger Price]

On Fri, 12 Mar 2021, Douglas Parsons wrote:

> Initiator in place of manager also works. So initiator/subscriber.
> But manager will likely be better recieved.

The I-D currently uses "Attachment Daemon" as a generic term for upsd, and 
"Management Daemon" as a generic term for the upsmon, upsrw, ... clients.

If the list considers "manager" to be better than "primary", then it would 
probably be clearer to replace "Management Daemon" by "Client Daemon".

Perhaps "secondary" could become "doer".

Roger