Assign a Working Time Arrangement to an Employee

<Warning> You may not benefit from this feature. Working-time-arrangements are the replacement for the workcycles. If this feature has not been deployed on your environment, please contact our support. </Warning>

Assigns a new working time arrangement to a single employee, effective from the specified start date (assignmentStart).

This operation will:

1. End the current assignment with an end date set to the eve of assignmentStart.
2. Create a work-contract amendment for the employee at assignmentStart, that gives them the new working time arrangement.