Update NUT submodule to v2.7.2
projects: update walNUT description

As of walNUT's e396caa93db28680564ff69b820830857d08a046, it doesn't rely any longer on ups{c,cmd,rw}, but uses instead a GJS implementation of NUT's net protocol.
Update NUT submodule
Add mge-usb-rj45.jpg to the list of cable images

As per NUT's fe04d7d46eee507d6c46f79320a853f024cff3a2