Register component for republish node in humble

[khughes-bdai]

On the rolling branch, a component is registered for the republish node (source):

#include "rclcpp_components/register_node_macro.hpp"

// Register the component with class_loader.
// This acts as a sort of entry point, allowing the component to be discoverable when its library
// is being loaded into a running process.
RCLCPP_COMPONENTS_REGISTER_NODE(image_transport::Republisher)

I would like to be able to use this in humble, but the component is not registered on that branch (source)