Drop support for Go 1.21 in dice example (#5800)

Resolves #5359

example/dice/rolldice.go

@@ -4,8 +4,15 @@
 package main
 
 import (
+	"fmt"
+	"io"
+	"math/rand"
+	"net/http"
+	"strconv"
+
 	"go.opentelemetry.io/contrib/bridges/otelslog"
 	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/metric"
 )
 
@@ -27,3 +34,27 @@ func init() {
 		panic(err)
 	}
 }
+
+func rolldice(w http.ResponseWriter, r *http.Request) {
+	ctx, span := tracer.Start(r.Context(), "roll")
+	defer span.End()
+
+	roll := 1 + rand.Intn(6)
+
+	var msg string
+	if player := r.PathValue("player"); player != "" {
+		msg = fmt.Sprintf("%s is rolling the dice", player)
+	} else {
+		msg = "Anonymous player is rolling the dice"
+	}
+	logger.InfoContext(ctx, msg, "result", roll)
+
+	rollValueAttr := attribute.Int("roll.value", roll)
+	span.SetAttributes(rollValueAttr)
+	rollCnt.Add(ctx, 1, metric.WithAttributes(rollValueAttr))
+
+	resp := strconv.Itoa(roll) + "\n"
+	if _, err := io.WriteString(w, resp); err != nil {
+		logger.ErrorContext(ctx, "Write failed", "error", err)
+	}
+}