Replace UPS apcupsd with NUT with usbhid-ups support

[rioachim]

Status:

• latest USB APC UPS firmwares no longer work properly with apcupsd, the apcupsd service loses communication with UPS after some minutes and log is flooded by "hid-core.c: control queue full" or "battery disconnected/UPS battery must be replaced/Battery reattached" ( APC Back-UPS BX1600MI spurious LOWBATT/REPLACEBATT events networkupstools/nut#2347 ).
• previous APC firmwares work fine (before 2023), but the latest ones (2023 onwards) don't because the UPS now sends a series of messages [OL DISCHRG CHRG LB RB] as calibration
• apcupsd 3.14.14 is no longer updated since 2016 and was compatible with APC only anyway

Suggestion:

• replace apcupsd with NUT which is actively supported ( https://networkupstools.org/ )
• USBHID driver is sufficient as base ( https://networkupstools.org/docs/man/usbhid-ups.html )
• NUT is compatible with 180 different manufacturers, and 1180 hardware UPS device models ( https://networkupstools.org/stable-hcl.html )
• NUT is similar to apcupsd ( https://networkupstools.org/docs/man/apcupsd-ups.html )
• NUT support already exists in OpenWRT ( https://openwrt.org/docs/guide-user/services/ups/software.nut )
• NUT is available on Entware ( http://bin.entware.net/armv7sf-k2.6/nut_2.8.0-3_armv7-2.6.ipk )