public class ConfigurationSubscription
ConfigurationSubscription publishes a reloading, thread-safe view of file configuration. The class
periodically calls FileConfiguration.reload on the underlying conf, and propagates changes to the
concurrent config. The configured FileChangedReloadingStrategy ensures that file config will only
be reloaded if something changed.
1. Reload schedule is never terminated. The assumption is a finite number of these are started
at the calling layer, and terminated only once the executor service is shut down.
2. The underlying FileConfiguration is not at all thread-safe, so its important to ensure access
to this object is always single threaded.