This makes a few things easier. You could see None as being a signalling value to indicate that we don't know capabilities, but this signalling would get lost anyway in the serialising to the metadata. So just an empty list is fine for now.
Contributes to issue CURA-8671.
This makes the cluster size also available when the machine is offline.
Also fixes an issue where the cluster size is improperly restored
once the internet connection comes back online, resulting in the printer
showing as a single printer until next sync
CURA-7347