sysutils/nut: Only one UPS supported at a time

[yodaldevoid]

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Is your feature request related to a problem? Please describe.
Due to the use of a single, global UPS name field, only one local UPS may be used at a time. Technically a remote netclient monitor can also be used, but it also uses the same UPS name field, so use is limited.

This disallows the use of redundant UPS systems, and other more complex setups, with the NUT plugin.

Describe the solution you'd like
A user should be allowed to define as many local UPS drivers as they would like, each with a different name. A lit of UPSs, like what is done for firewall rules, would be perfect.

Describe alternatives you've considered
The plugin could be ignored completely and NUT configured manually.

[Monviech]

The maintainer of the plugin is @mimugmail , let's wait for a response if a big overhaul is wanted first.