Documentation note for gltf loader API

Documentation/release/dev/gltf-toggle-data.md

+## GLTF document loader selectively toggle model data
+
+The `vtkGLTFDocumentLoader` learned to selectively enable/disable loading of certain types of model
+data from the gltf file. The loader exposes the following new API:
+
+  - `SetLoadAnimation(bool)`: Load animation keyframes (default: true)
+  - `SetLoadImages(bool)`: Load model images (default: true)
+  - `SetLoadSkinMatrix(bool)`: Load inverse bind matrices for model Skin (default: true)