Example image of 3 transforms are missing in API doc

[Nic-Ma]

Is your feature request related to a problem? Please describe.
After #3491 , I check all the other categories of transforms in the API doc, I think we only have 3 transforms left that need example image:

1. Spatial transform: GridDistortion
2. Smooth field transform: RandSmoothFieldAdjustContrast
3. Smooth field transform: RandSmoothFieldAdjustIntensity

Would be nice to add example images for them.