Expand timedMetrics to track additional granularity

[tobyhei]

https://github.com/seek-oss/datadog-custom-metrics#createtimedspan only tracks up the 95th percentile as it uses Datadog histograms instead of distributions. https://docs.datadoghq.com/developers/metrics/types/?tab=distribution#metric-types

My use case for the 99th percentile is being able to track where application time is spent where load balancer alarms are set for the 99th percentile response time.