Use as Terrain Tileset Base Layer button missing

[r-veenstra]

The Use as Terrain Tileset Base Layer button in the Assets UI appears to be missing for Imagery assets.

https://community.cesium.com/t/geotiff-data-can-no-longer-be-linked-to-omniverse/30363

An initial test reproduction:

• Add Cesium World Terrain to stage using the Add to Stage button in the assets UI
• Select an Imagery asset in the assets UI - No button appears for adding the layer