rate_moving_average and rate_moving_average_and_histogram are type that
are used by the JMX. They are based on the yammer meter and timer and
are used to collect derivative information.
Specificlly: rate_moving_average calculate rates and
rate_moving_average_and_histogram collect rates and
histogram.
Signed-off-by: Amnon Heiman <amnon@scylladb.com>