MetricsToRead returns a map of MetricStats that match the criteria expressed in the ExportConfigs.

ReadMetrics pulls metrics for the passed time over the period of duration into the metricstats map.

NaN will set the stat to not-a-number.

Prior leaves the stat set to its prior value; this is the default.

Zero will set the stat to 0.

ExportConfig describes which cloudwatch metrics we want to export.

MetricStat is a specific statistic for a *cloudwatch.Metric with a related, registered *prometheus.Gauge.

StatDefaultType describes how to deal with a stat that has no value.