The set of label values that uniquely identify this timeseries. Applies to
all points. The order of label values must match that of label keys in the
metric descriptor.
Must be present for cumulative metrics. The time when the cumulative value
was reset to zero. Exclusive. The cumulative value is over the time
interval (start_timestamp, timestamp]. If not specified, the backend can
use the previous recorded value.
A collection of data points that describes the time-varying values of a metric.