Allow users to specify sensor network names

Prometheus samples are currently reported using the circuit network ID as a label. This works, but doesn't provide a great user experience.

Ideally, users could set the "sensor network name" of each individual sensor (using a UI similar to [Attach Notes](https://mods.factorio.com/mod/attach-notes)), and we would report samples using the network name as a label. This also lets users "combine" related sensor readings by setting sensors to have the same network name.