Hydra Storm: prepare for MaterialX export support

Does nothing yet, but will once blender/blender#111765 lands.

Pull Request: https://projects.blender.org/blender/blender-addons/pulls/104859

Author: bnagirniak

hydra_storm/engine.py

@@ -12,6 +12,7 @@ class StormHydraRenderEngine(bpy.types.HydraRenderEngine):
 
     bl_use_preview = True
     bl_use_gpu_context = True
+    bl_use_materialx = True
 
     bl_delegate_id = 'HdStormRendererPlugin'