RAP-1116 Use LINC's automated demixing approach

This MR adds the automated demixing workflow from LINC into the pre-processing pipeline. With this change the pre-processing pipeline there's a slight breaking change in interface, because of the way the automated demixing approach is implemented.

This functionality is added to the prepare_input.cwl workflow, and samples (semi-randomly?) three measurement sets from the ones provided to determine optimal demixing parameters. Hence, ideally the pipeline is run with all measurement sets. (Or at least 3.) This is a change from the old behaviour, where one could run the pipeline on a single MS.