launch_testing integration

[romainreignier]

I have tried to do some integration testing on my Rust ROS 2 nodes.
By following the launch_testing tutorial I have managed to write a Python script launching my node and testing it.
I can run it with:

$ launch_test test/test_my_node.py

Now I need the equivalent of Register the test in the CMakeLists.txt part to be able to run it with colcon test.

How can we achieve this with ros2_rust?