Update `NewRelicProperties` so that the event type sent with each
metric can be configured. An additional `boolean` property has
also been added if the previous behavior using the "meter-name"
is required.

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 "SpringBootSample" category. When doing so,
additional context is provided by including "metricName" and
"metricType" attributes.

See gh-18472