Implement sum of squared deviations for exponential histograms

[dashpole]

Similar to the implementation for histograms, we should create a sum of squared deviations for exponential histograms:

opentelemetry-operations-go/exporter/collector/metrics.go

Lines 1034 to 1046 in 3cec368

	if m.cfg.MetricConfig.EnableSumOfSquaredDeviation {
	// Calculate the sum of squared deviation.
	for i := 0; i < bounds.Len(); i++ {
	// Assume all points in the bucket occur at the middle of the bucket range
	middleOfBucket := (prevBound + bounds.At(i)) / 2
	deviation += float64(counts[i]) * (middleOfBucket - mean) * (middleOfBucket - mean)
	prevBound = bounds.At(i)
	}
	// The infinity bucket is an implicit +Inf bound after the list of explicit bounds.
	// Assume points in the infinity bucket are at the top of the previous bucket
	middleOfInfBucket := prevBound
	deviation += float64(counts[len(counts)-1]) * (middleOfInfBucket - mean) * (middleOfInfBucket - mean)
	}

It should be implemented here:

opentelemetry-operations-go/exporter/collector/metrics.go

Line 1069 in 3cec368

func (m *metricMapper) exponentialHistogramPoint(point pmetric.ExponentialHistogramDataPoint, projectID string) *monitoringpb.TypedValue {