feat: add getting visitor counter

internal/handler/visitor.go

@@ -0,0 +1,18 @@
+package handler
+
+import (
+	"backend/internal/service"
+	"encoding/json"
+	"net/http"
+)
+
+func HandleGetVisitorCounter(w http.ResponseWriter, r *http.Request) {
+	data := service.GetVisitorCounter()
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(data)
+}
+
+func HandlePatchVisitorCounter(w http.ResponseWriter, r *http.Request) {
+	w.Write([]byte("hello world"))
+}