Should CreateFromColorAndDepth()'s convert_rgb_to_intensity set to false by default?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### Proposed new feature or change

Consider the following code:

```python
import open3d as o3d
dataset = o3d.data.SampleRedwoodRGBDImages()
im_color = o3d.io.read_image(dataset.color_paths[0])
im_depth = o3d.io.read_image(dataset.depth_paths[0])
im_rgbd = o3d.geometry.RGBDImage.create_from_color_and_depth(im_color, im_depth)
```

You might assume that `im_rgbd` contains R, G, B, and depth. However, `create_from_color_and_depth`'s default argument converts RGB into grayscale. This is unintuitive, since the result is an "RGBD Image" object, however, we're getting an "Intensity Depth Image".

### References

_No response_

### Additional information

_No response_