ROS2 bag play include clock if not in bag

[4lon]

Description

Currently, if --clock is used, a /clock topic in a bag will be ignored. My suggestion is that a new flag be added, something like --clock-if-missing. This feature would add a /clock topic if none is in the recording, but if there already is a clock topic in the bag, it would just publish the bag's clock topic. I think this would be helpful for streamlining reusability of commands when playing against a simulation or real robot data.

Completion Criteria

• New flag added to ros2 bag play that implements this feature.

Implementation Notes / Suggestions

I don't have any further implementation suggestions, other than I am happy to work on this. I think one of the more complicated parts of this feature is to determine how it should interact with the --clock-topics and --clock-topics-all flags. I don't know what the current implementation does if --clock isn't specified but --clock-topics is, because I can imagine that being equivalent behavior.