some optimization

src/users/get_all_users.cpp

@@ -33,7 +33,7 @@ void get_all_users(const httplib::Request& request, httplib::Response& response)
         syslog(LOG_ERR, "access reject in get all user request");
         return;
     }
-    std::ifstream usersfile("users.json");
+    std::ifstream usersfile(USERS_FILE);
     nlohmann::json all_users = nlohmann::json::parse(usersfile);
     usersfile.close();
     nlohmann::json response_user_data = nullptr;