* Match machines by MAC address in examples
* Re-use the MAC address to assign static networkd configs
where needed.
* UUID is useful to uniquely identify a machine (unlike MAC)
but many users had difficulty finding the network device name
to use in static networkd configs. Selecting by MAC reduces
the potential for user error here.
* Split config.yaml files into JSON groups files
* Update examples to use folders of mountable groups files
* Stop reading groups from a -config config.yaml file
* Add RichGroup JSON <-> Protobuf Serialize Group
