add metrics support

[jgilbert01]

• size of batch
• pipeline start and end timer
• eventType ratio
• other
• cw, datadog, other
• toPromise2 that returns metrics
• dynamodb capacity units?
• enable/disable via global/local options ?

[petermyers]

In addition to what you listed above:

• Lambda Xray integration
• New relic?
• Memory cache hits / misses
• Timing data - beyond just start and end timers for the pipeline, I'm thinking about enabling performance profiling. A utility you wrap pipeline steps in that adds additional timing data at a more granular level
• Pipeline ratios for batch - More so than just eventTypes since in practice a single event type might get processed by multiple pipelines

[jgilbert01]

• defines a standard "metrics" field on uow
• sinks/queries/steps/etc will add metrics as appropriate to the uow
• a new toPromiseWithMetrics which will create histograms from uow.metrics per pipeline with min/avg/max/etc
• and write the metrics as cloudwatch logs embedded metrics
• https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Embedded_Metric_Format_Specification.html
• return subset of metrics instead of Success

[petermyers]

Can we call this issue resolved at this point?