Add star-shapes-mk2 exercise

Now improved using methods and interfaces!

star-shapes-mk2/go.mod

@@ -0,0 +1,3 @@
+module star-shapes-mk2
+
+go 1.22.2

star-shapes-mk2/main.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+)
+
+type Shaper interface {
+	Shape(int) Square
+}
+
+type Square struct {
+	form     string
+	quantity int
+}
+
+func (s Square) Shape(num int) Square {
+	for i := 0; i < num; i++ {
+		for i := 0; i < num; i++ {
+			s.form += "* "
+		}
+		s.form += "\n"
+	}
+
+	s.quantity = num
+	return s
+}
+
+func showShape(s Shaper, num int) {
+	fmt.Println(s.Shape(num).form)
+}
+
+func getNumberStars() int {
+	numStr := os.Args[1]
+	num, err := strconv.Atoi(numStr)
+	if err != nil {
+		log.Panicln(err)
+	}
+	return num
+}
+
+func main() {
+	s := Square{}
+	showShape(s, getNumberStars())
+}