Add 'repetition' example using ForLoop action

[christophebedard]

This adds an example that is similar to the recursion example but using the new launch ForLoop action. See:

1. Add ForEach action to repeat entities using iteration-specific values ros2/launch#802
2. https://discourse.ros.org/t/requesting-feedback-new-for-loop-action-for-ros-2-launch-files-to-repeat-entities/42021/5

Note that I tried to find the ForLoop/ForEach API docs (based on the Python class docstring I made sure to add in the original PR), but it's not there: https://docs.ros.org/en/rolling/p/launch/launch.actions.html#submodules. That is obviously bad and I hope to improve that. However, in parallel, I'm trying to update examples I see out in the wild to use ForLoop/ForEach, e.g., in Nav2: ros-navigation/navigation2#4990 / ros-navigation/navigation2#5000.

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Open questions:

1. Should I replace the recursion example with this and call it repetition? From my understanding, the goal is repetition; recursion was the method.
2. The current recursion example uses [N, 1], but ForLoop does [0, N) by default. Do you want me to use str(10 - i) to reverse it and get [N, 1]?