[Bug Report] `root_height_below_minimum` is not supported for rough terrain

[hany606]

Describe the bug

The termination function of root_height_below_minimum is only supported for flat terrain. It does not consider training in rough terrains, such as Inverted Pyramid Stairs Terrain, as the asset starts from a base placed below the flat terrain level.

Checklist

• I have checked that there is no similar issue in the repo (required)
• I have checked that the issue is not in running Isaac Sim itself and is related to the repo

[RandomOakForest]

Thank you for posting this and adding the PR. The team will review it. Note that this may be tagged as a feature request. Thank you.