Added incompatible event support to ros2 topic echo and ros2 topic pub

[jaisontj]

Depends on ros2/rclpy:459

Related to the feature discussed here. This PR handles the ON_REQUESTED_INCOMPATIBLE_QOS and ON_OFFERED_INCOMPATIBLE_QOS callback events on ros2 topic echo and ros2 topic pub commands respectively.

This way, users now will get a warning when they echo/pub to a topic with incompatible QoS Policies.

Signed-off-by: Jaison Titus jaisontj92@gmail.com

[mm318]

@jaisontj, @ivanpauno, @wjwwood, can any of you bring this pull request out of draft mode?

[ivanpauno]

Left some minor comments, LGTM!

[Karsten1987]

This change calls rmw_create_publisher twice per topic on the same node. In the case of DDS (tested on FastRTPS only) this might work well, but other RMW implementations, i.e. iceoryx might not support this.

Is there a way that the publisher is called only once? Meaning, can the QoS event checked somewhat before creating a publisher?

[mm318]

We could add an option to rclcpp's and rclpy's create_publisher()/create_subscription() to ignore registering callbacks of unsupported event types, instead of throwing and retrying to create_publisher()/create_subscription() at the client level.