Not compatible with ROS2 Foxy

[AntoineHX]

I believe this package is only compiling against ROS2 Galactic (or newer distributions) since it's using rclcpp::GenericSubscription which are only part of rosbag2_transport package (included in rosbag2 foxy branch).

It would be nice to support Foxy, if possible. Furthermore, it might be useful to precise which ROS2 version are compatible.

[JWhitleyWork]

Only Galactic and above is supported and this is unlikely to change unless someone else does a port. GAIA is now defunct so I doubt too many people are watching this repo.