Introduce trace verbosity config and produce less spans by default

pkg/middlewares/observability/semconv_test.go

@@ -83,6 +83,11 @@ func TestSemConvServerMetrics(t *testing.T) {
 			handler, err = capture.Wrap(handler)
 			require.NoError(t, err)
 
+			// Injection of the observability variables in the request context.
+			handler = WithObservabilityHandler(handler, Observability{
+				SemConvMetricsEnabled: true,
+			})
+
 			handler.ServeHTTP(rw, req)
 
 			got := metricdata.ResourceMetrics{}