"Re-stamper" that takes an input topic and sets its header timestamp to ROS now #130

Description

Change the header.stamp to get_clock().now() on messages coming through this transformer

I think this is possible out of the box with the transform tool, but I feel its a pretty common use case for, say, sensor data from bag playback into a live-running TF system.

Implementation Notes / Suggestions

Not sure if this is possible in C++, in which case it would have limited utility given the performance and latency problems of Python nodes on large messages

Testing Notes / Suggestions