Adding support for Kilovault HLX+

[alexphredorg]

Kilovault batteries were pretty popular in both the solar and marine communites, with good reviews on Panbo and other major blogs. Unfortunately the US company that owned them (AltE Store) closed with very little notice. The batteries themselves were made by TopBand.

The driver submitted uses BLE. There is no protocol documentation available, but I started with some work by github user @fancygaphtrn and I had a working old copy of the app on my phone. Using his code I was able to write a simulator that allowed me to trick the phone app into talking to a Mock battery, and used that to figure out the remaining unknown fields in the BLE status messages. That code can be found here: https://github.com/alexphredorg/kvbms/tree/main

The batteries also have CAN support, but Kilovault told me that it would require a firmware upgrade to use it. I can confirm by sniffing the CAN port that it isn't functional today, it just sends a 2-byte hello sequence once per second.

I've submitted a PR with a working driver, tested on a HLX+1200. That can be found here:
#183

Doc updates are here:
mr-manuel/venus-os_dbus-serialbattery_docs#4

[mr-manuel]

Nice work!