Add distribution and histogram metric support

[nlehrer]

Only non-distribution (bool, int64, double, etc.) values are supported by the exporter at the moment. See this line of code for the relevant TODO and where support should be added (perhaps among other places).

[nlehrer]

Check if a distribution without buckets is rejected by the API.

[coreyvan]

Are histograms and distribution metric kinds supported now? I noticed that a fix got merged in as part of #125 but there's still this method that sets the MetricKind to UNSPECIFIED (which causes GCP to reject the metric descriptor) here:

opentelemetry-operations-js/packages/opentelemetry-cloud-monitoring-exporter/src/transform.ts

Lines 72 to 85 in 60f90dc

	function transformMetricKind(kind: OTMetricKind): MetricKind {
	switch (kind) {
	case OTMetricKind.COUNTER:
	case OTMetricKind.OBSERVABLE_COUNTER:
	return MetricKind.CUMULATIVE;
	case OTMetricKind.UP_DOWN_COUNTER:
	case OTMetricKind.OBSERVABLE_GAUGE:
	case OTMetricKind.OBSERVABLE_UP_DOWN_COUNTER:
	return MetricKind.GAUGE;
	default:
	// TODO: Add support for OTMetricKind.HISTOGRAM
	return MetricKind.UNSPECIFIED;
	}
	}

[nlehrer]

It does seem from that code that it is still not supported but that it could be easy to complete the support. A new owner needs to be found for this issue since @TigerHe7 is no longer working on this project (neither am I).