simulation time in log messages

[asherikov]

ROS1 could output log messages with simulation clock timestamps http://wiki.ros.org/rosconsole#Console_Output_Formatting, which does not seem to be supported in ROS2 https://github.com/ros2/rcutils/blob/rolling/include/rcutils/logging.h#L62, but could be useful.

[fujitatomoya]

IMO this can be useful for the application that uses simulation clock.

currently this is not supported, rcutils logging macro is not aware of simulation time (nor node object), so the application needs to fill the simulation clock time in the logging data payload with their responsibility. client logging macros (rclcpp, rclpy and rcl) are actually aliases to rcutils logging macros. So for doing this, client logging macros need to be responsible to fetch the simulation clock if that is available, and fill that in the logging data payload and formatted by rcutils. (i am not sure if this is the best way to do that, but something i think of.)