Move ML processes to 2.1.0

[m-mohr]

As they are very unstable and a lot of discussions are still ongoing, I'd propose to remove the ML-related processes from the 2.0.0 release branch and keep them in a separate branch for 2.1.0.

[soxofaan]

should we also remove fit_curve (which is also some kind of ML process)?
(also see #425)

[m-mohr]

no, fit_curve was already included in the 1.2.0 release.