[Qhull] Move usage into own function

[maxfirmbach]

Description

We should move Qhull calls into dedicated functions away from the place of use (for example as we do with ArborX). This should give us better control of the third-party library.

In a second step we should think about making it an optional dependency. Qhull is only used in one place in cut. Users should not need to build 4C with Qhull just to be able to use cut related functionality, which would ease the installation process in many cases.

Possible Solution and Definition of Done

• Move Qhull calls into dedicated functions away from its actual use (e.g. somewhere in core being called convex_hull() or similar)
• Make Qhull an optional dependency