Added mg_bt

mg_bt/src/mg_bt.cpp

@@ -0,0 +1,23 @@
+#include <iostream>
+
+#include "mg_tree_executor.hpp"
+
+int main(const int argc, const char** argv) {
+    rclcpp::init(argc, argv);
+
+    std::cout << "Starting up Behavior Tree Executor" << std::endl;
+
+    rclcpp::NodeOptions options;
+
+    auto bt_exec_server = std::make_shared<mg::MgTreeExecutor>(options);
+
+    rclcpp::executors::MultiThreadedExecutor executor(
+      rclcpp::ExecutorOptions(), 0, false, std::chrono::milliseconds(250));
+
+    executor.add_node(bt_exec_server->node());
+    executor.spin();
+    executor.remove_node(bt_exec_server->node());
+
+    rclcpp::shutdown();
+    return 0;
+}