FastGlobalRegistrationOption decrese_mu default is set to False

### 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 noticed that the default value for decrease_mu in FastGlobalRegistrationOption is set to False as default.
I'm not sure if this is expected, as I understand from the FGR paper the graduated non-convexity is an important part of the algorithm and I think that not using it as default is a bug.

### Steps to reproduce the bug

```python
import open3d
test1 = open3d.pipelines.registration.FastGlobalRegistrationOption(decrease_mu=True)
test2 = open3d.pipelines.registration.FastGlobalRegistrationOption(decrease_mu=False)
test3 = open3d.pipelines.registration.FastGlobalRegistrationOption()
print(test1.decrease_mu == test3.decrease_mu)
print(test2.decrease_mu == test3.decrease_mu)
```

### Error message

_No response_

### Expected behavior

_No response_

### Open3D, Python and System information

```markdown
- Python version: Python 3.6.9
- Open3D version: 0.15.2
```

### Additional information

_No response_