Add default Incompatible QoS callbacks

[mm318]

Feature request

Feature description

With #459 merged in, a user is able to provide a callback for when an participant on the topic is discovered but unable to be matched due to incompatible QoS policies. This feature request is for leveraging this feature even when a user does not provide a custom callback function, by setting a default callback function that prints a warning (initially suggested at ros2/ros2#822 (comment)) on the discovery of an incompatible participant on the topic.

Implementation considerations

What should the behavior be if the underlying middleware does not support this kind of QoS event callback?

[hidmic]

@mm318 are you looking forward to implement this feature?

[mm318]

Hi @hidmic, we already have a pull request opened for this at #536.

[mm318]

Closing this issue as the related pull request has been merged.