A service that watches the clusternode table for node state changes and emits appropriate events.
Note that it only sends a NodeRemovedFromClusterEvent if the node has shutdown cleanly and entered the OFFLINE
state. It does not send events about nodes leaving the cluster without notification, e.g. due to network
partitions or shutting down abruptly.
Note that it also notifies of changes to the current node, and it is up to the events' consumers to decide
how to treat those.