Bounding box properties inconsistency

### 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).

### Describe the issue

I have noticed, that there is inconsistency between oriented bounding box and axis aligned bounding box. In the AxisAlignedBoundingBox you have get function for getting extent, in the OrientedBoundingBox, you have property.

Also, OrientedBoundingBox has both get_center function and center property.

### Steps to reproduce the bug

```python
Link to AxisAlignedBoundingBox get_extent:
http://www.open3d.org/docs/latest/python_api/open3d.geometry.AxisAlignedBoundingBox.html#open3d.geometry.AxisAlignedBoundingBox.get_extent

vs.

Link to OrientedBoundingBox extent:
oriented: http://www.open3d.org/docs/latest/python_api/open3d.geometry.OrientedBoundingBox.html#open3d.geometry.OrientedBoundingBox.extent
-------------------------------------------

Link to OrientedBoundingBox get_center:
http://www.open3d.org/docs/latest/python_api/open3d.geometry.OrientedBoundingBox.html#open3d.geometry.OrientedBoundingBox.get_center

vs.

Link to OrientedBoundingBox center:
center: http://www.open3d.org/docs/latest/python_api/open3d.geometry.OrientedBoundingBox.html#open3d.geometry.OrientedBoundingBox.center
```

### Error message

_No response_

### Expected behavior

_No response_

### Open3D, Python and System information

```markdown
- Operating system: Kubuntu 21.10
- Python version: Python 3.9.7
- Open3D version: 0.14.1+816263b (it is also in documentation for 15.1)
- System architecture: x86
- Is this a remote workstation?: no
- How did you install Open3D?: pip (dev branch)
- Compiler version (if built from source): gcc 11.2.0
```

### Additional information

_No response_