[visualization] declare warehouse params in rviz plugin

The Motion planning plugin currently ignores parameters for warehouse_ros,
because they are not declared yet.
This can be verified by launching `ros2 launch run_move_group run_move_group.launch.py`
(where some warehouse parameters like `warehouse_plugin` have to be defined before)
and examinig the parameters with `ros2 param dump rviz2`.

moveit_ros/visualization/motion_planning_rviz_plugin/src/motion_planning_display.cpp

@@ -207,6 +207,14 @@ void MotionPlanningDisplay::onInitialize()
 {
   PlanningSceneDisplay::onInitialize();
 
+  // Prepare database parameters
+  if (!node_->has_parameter("warehouse_host"))
+    node_->declare_parameter<std::string>("warehouse_host", "127.0.0.1");
+  if (!node_->has_parameter("warehouse_plugin"))
+    node_->declare_parameter<std::string>("warehouse_plugin", "warehouse_ros_mongo::MongoDatabaseConnection");
+  if (!node_->has_parameter("warehouse_port"))
+    node_->declare_parameter<int>("warehouse_port", 33829);
+
   // Planned Path Display
   trajectory_visual_->onInitialize(node_, planning_scene_node_, context_);
   QColor qcolor = attached_body_color_property_->getColor();