chore(new_relic sink): add distribution support and send metric type

[tobz]

In the new_relic sink, among other issues, we currently do not support distributions even though they're supported on the New Relic side. Additionally, we don't send the metric type, which causes all metrics -- counter or gauge -- to be treated as gauges.

We should:

• [new_relic sink] add a normalization layer to the sink to get incrementalized counters #13902
• [new_relic sink] actually set the metric type in the metrics API model object #13903
• [new_relic sink] send distributions to New Relic #13904

[jszwedko]

cc/ @asllop . I know you contributed the initial new_relic sink so just flagging this in case it is something you are interested to contribute.

[asllop]

@jszwedko yes I am! Also interested in #13377, I just don't know when I'm gonna have time to contribute.