Ros2 publish message command line

ros2 publish message command line

# ros2 topic pub --once <topic> <message type> <data>
ros2 topic pub --once /turtle1/cmd_vel geometry_msgs/msg/Twist "{linear: {x: 2.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 1.8}}"