[hw-7] add metrics, tracing

cart/internal/infra/http/middlewares/tracing.go

@@ -0,0 +1,17 @@
+package middlewares
+
+import (
+	"net/http"
+
+	"route256/cart/internal/infra/tracing"
+)
+
+func NewTracingMiddleware(h http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ctx, span := tracing.Tracer().Start(r.Context(),
+			r.Method+" "+r.URL.Path)
+		defer span.End()
+
+		h.ServeHTTP(w, r.WithContext(ctx))
+	})
+}