Sync recipe following a pivot recipe

Hi,

the sync recipe doesn't automatically propagate schema changes, so it will simply fill columns in its output dataset that exist in the input.

But actually, pivot is an outlier here. The overwhelming majority of recipes in DSS don't change their output schema. And that's because automatically updating schemas of datasets is a complicated operation, and very hard to get right.

If you need simple propagation, like what you get when you right-click on a dataset and do "propagate schema changes from here", you can use a scenario:

- start by building the output of the pivot recipe with a Build/train step, in mode "build only this dataset"

- use a propagate schema step

- build the rest of the flow with a Build/train step