Add section about label set presets to multilabel segmentation documentation
Summary:
Label set presets were recently introduced to the UI but not yet described in the documentation.
Fixes T27908.
Test Plan: Checked F1 help page of multilabel segmentation view.
Reviewers: O1 MITK Reviewer Group I, kalali
Reviewed By: O1 MITK Reviewer Group I, kalali
Maniphest Tasks: T27908
Differential Revision: https://phabricator.mitk.org/D437