Add support for categorical "MicrometerSample" eventType to publish New Relic metrics.

[neiljpowell]

Previous behavior was to publish an eventType per Meter/metric name
(still supported via meterNameEventTypeEnabled=true). NewRelic's own
agents publish metrics to eventTypes aligned with broader categories. To
align with their recommendation the default behavior is to publish
metrics under a "MicrometerSample" category. When doing so, additional
context is provided by including "metricName" and "metricType"
attributes. Also "timeUnit" is now provided as an attribute for all
Timer related metrics regardless, so Insights users can better
understand time-based metrics.
See: https://docs.newrelic.com/docs/insights/insights-data-sources/default-data/insights-default-data-other-new-relic-products

@shakuzen
@breedx-nr

[checketts]

It seems like you are still iterating on this PR. Please comment on it when you are ready for a review.

[neiljpowell]

@checketts Hi. It's now ready for review. I had recently upgraded my IDE and forgot to adjust the tab/space indentation settings. Resulted in the extra iterations.

[breedx-nr]

This looks like a good change to me, with just a few small/opinionated suggestions. I think this is an interesting step in making the existing Insights/event based exporter more useful.

It should also be noted that New Relic recently published an open source registry that supports dimensional metrics instead of events: https://github.com/newrelic/micrometer-registry-newrelic

[breedx-nr]

Thanks for the tweaks!

[shakuzen]

It should also be noted that New Relic recently published an open source registry that supports dimensional metrics instead of events: https://github.com/newrelic/micrometer-registry-newrelic

@breedx-nr That's great. I didn't know about that. Would you be willing to update our docs to mention this new option? Docs source is at https://github.com/micrometer-metrics/micrometer-docs/

[neiljpowell]

Ugh. io.micrometer.spring.autoconfigure.export.prometheus.PrometheusMetricsExportAutoConfigurationTest failures. @shakuzen my simple changes are failing to build due to unrelated errors. Thoughts?

[izeye]

It should also be noted that New Relic recently published an open source registry that supports dimensional metrics instead of events: https://github.com/newrelic/micrometer-registry-newrelic

@breedx-nr That's great. I didn't know about that. Would you be willing to update our docs to mention this new option? Docs source is at https://github.com/micrometer-metrics/micrometer-docs/

@shakuzen I created micrometer-metrics/micrometer-docs#102 to document it based on its README file.