implement proper lazy subscribers

[mikeferguson]

This is blocked by upstream work that should be included in Iron turtle - ros2/rmw#330 (comment)

[mikeferguson]

Started on this - it is an epic rabbit hole:

• We need to update image_proc/depth_proc to make this work (they aren't lazy, and they subscribe to our outputs)
• That means we need to update image_transport (which most of the image_proc subscribers use)
• That might also lead to changing things in message_filters, which image_transport uses (but so far, maybe not).

[mikeferguson]

Work in Progress:

• add support for lazy subscribers ros-perception/image_common#272
• add support for lazy subscribers ros-perception/image_pipeline#815
• https://github.com/ros-drivers/openni2_camera/tree/proper_lazy_subs (will open a PR here once the image_common stuff is merged & released, since that is very much required)

[mikeferguson]

As a note - this will NOT make it into Iron, since we can't get the image_common changes merged into Iron (apparently that package is part of the base and was frozen on April 17). I will continue to get this merged into rolling, but it won't make into a regular release until 2024

[mikeferguson]

image_pipeline is now updated - but not yet released