Now its plain updateable_value, but without the ..._source object the
updateable_value is just a no-op value holder. In order for the
observers to operate there must be the value source, updating it would
update the attached updateable values _and_ notify the observers.
In order for the config to be the u.v._source, config entries should be
comparable to each other, thus the <=> operator for it
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
210b01a5ce