Fix: correct the value of otelcol_exporter_send_failed_requests

[ralphgj]

The metric of otelcol_exporter_send_failed_requests defined in obsreportconfig.go used view.Count() as the aggregation.

	errorNumberView := &view.View{
		Name:        obsmetrics.ExporterPrefix + "send_failed_requests",
		Description: "number of times exporters failed to send requests to the destination",
		Measure:     obsmetrics.ExporterFailedToSendSpans,
		Aggregation: view.Count(),
	}

In obsreport_exporter.go, while numFailedToSend(obsmetrics.ExporterFailedToSendSpans) equals 0, it will also increase count of the metric. The actual meaning of otelcol_exporter_send_failed_requests is the total count of requests that sent to destination but not the failed requests.

func (exp *Exporter) recordMetrics(ctx context.Context, numSent, numFailedToSend int64, sentMeasure, failedToSendMeasure *stats.Int64Measure) {
	if obsreportconfig.Level() == configtelemetry.LevelNone {
		return
	}
	// Ignore the error for now. This should not happen.
	_ = stats.RecordWithTags(ctx, exp.mutators, sentMeasure.M(numSent), failedToSendMeasure.M(numFailedToSend))
}

[bogdandrutu]

@alolita I remember this metric was added to help some AWS health extension. Does this fix affects you?

[codecov]

Codecov Report

Merging #4629 (5e27ca4) into main (f13a011) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #4629      +/-   ##
==========================================
+ Coverage   90.44%   90.46%   +0.02%     
==========================================
  Files         181      181              
  Lines       10598    10611      +13     
==========================================
+ Hits         9585     9599      +14     
+ Misses        789      788       -1     
  Partials      224      224              

Impacted Files	Coverage Δ
obsreport/obsreport_exporter.go	94.44% <100.00%> (+0.44%)	⬆️
obsreport/obsreporttest/obsreporttest.go	95.58% <100.00%> (+1.10%)	⬆️

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