Add newton-usd-schemas

[andrewkaufman]

Is this a new feature, an improvement, or a change to existing functionality?

New Feature

Feature Description

Add newton-usd-schemas as a dependency & apply the schemas, but don't author any opinions unless they map directly to URDF concepts.

Additional context or alternatives

By applying the schemas it makes authoring opinions in downstream tools (e.g. Isaac Sim) easier.

Code of Conduct

• I agree to follow urdf-usd-converter Code of Conduct
• I have searched the open issues and have found no duplicates

[andrewkaufman]

I'm marking this blocked until newton-physics/mujoco-usd-converter#40 is complete, so we have a precedent for how to approach it.