Get last Isaac Sim version at launch time

[mcres]

The suggestion I propose is stated in the NVIDIA Forum:

Based on the assumption that most of the users only have a single Isaac Sim version installed, wouldn’t it be better to use whatever version is installed if the user does not specify any? In case the user has several versions installed, simply use the most recent one.

This way, people using ROS2 launch files with isaacsim would find it easier to use, since no version argument would need to be specified.