[Feature]: Add MJCF option to skip loading ground plane.

[vybhav-ibr]

Bug Description

in the latest main when spawning using MJCF morphs, i think this issue was fixed previously.
Because of this some robots start with their links penetrating the ground if not dealt with properly this will causes NaNs in the simulation

Steps to Reproduce

spawn the 'ant' xml asset from teh genesis assets

Expected Behavior

the ground plane be removed

Screenshots/Videos

Release version or Commit ID

latest main

Additional Context

No response

[duburcqa]

Can you provide a self-contained repro? I remember fixing this indeed.

[duburcqa]

the ground plane be removed

We are not going to silently remove the ground plane. it is part of the MJCF file. This would not be correct. But maybe we could add some opt-in morph option to remove any fixed ground plane at the root of MJCF file. If it was excluded at some point, it was a bug, not a feature.

[vybhav-ibr]

Huh, i must have used a different asset,
It would still be good to add an option to remove any planes, this will make xml files easier to work with