Add request count metric with status code label

Signed-off-by: m.nabokikh <maksim.nabokikh@flant.com>

CHANGELOG.md

@@ -13,6 +13,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Added
 
 - The project is now tested against Go 1.18 (in addition to the existing 1.16 and 1.17) (#1976)
+- Add the HTTP status code label to `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp` instrumentation that allows to count requests by their response code. (#771, #2138)
 
 ### Changed
 

instrumentation/net/http/otelhttp/handler.go

@@ -200,7 +200,9 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// Use floating point division here for higher precision (instead of Millisecond method).
 	elapsedTime := float64(time.Since(requestStartTime)) / float64(time.Millisecond)
 
-	h.valueRecorders[ServerLatency].Record(ctx, elapsedTime, attributes...)
+	// Status code label is required to count the errors ratio
+	durationAttributes := append(attributes, semconv.HTTPStatusCodeKey.Int(rww.statusCode))
+	h.valueRecorders[ServerLatency].Record(ctx, elapsedTime, durationAttributes...)
 }
 
 func setAfterServeAttributes(span trace.Span, read, wrote int64, statusCode int, rerr, werr error) {