Add an ups.conf toggle for voltage multipliers

[jimklimov]

battery.voltage: 1.3
battery.voltage.nominal: 1.2
is this a bug? I thought that voltage should be a bit higher.

The original post by @gyulaasztalos in #616 (comment) experimented with neutering of divide_by_10_conversion() and legrand_times10M_info() in the mapping tables.

This issue is about adding a configuration toggle (and perhaps ways of guessing a default if not specified - e.g. based on some mapping of device/model/firmware... identifiers) to report original voltages or factor them. Seems to be a common problem for many vendors, and sometimes for same brand/model devices with different HW/FW releases...

Note that currently not many drivers (or mapping tables where used) suggest having such a multiplication/division at all. For those that do, if we guess a default value - log this, with a suggestion to use the toggle if numbers seem off the target.

Loosely related to #1279 / #1652 area as well.