open3d required in source recon package

[cgohil8]

open3d is used in the osl.source_recon package. It needs to be added to the requirements here:

https://github.com/OHBA-analysis/osl/blob/main/setup.py#L11-L17

[cgohil8]

open3d is only used in the visualisation of coreg, specifically only when we include the nose. For the workshop we don't necessarily need this features. Therefore, we decided we will make open3d a soft requirement - i.e. not installed by default by the package and avoid including the nose when plotting the coreg.

[matsvanes]

We can add a decorator to coreg_display to check if open3d has been installed, if not, default include_nose in the coreg plotting to False.