Add LeaderOccupation to prevent leadership vehicles being sent to another simulated region #1094
Description
The vehicle the current leader belongs to does not get any occupation assigned. Hence, the vehicle of the current leader can be used for other activities like being sent from the staging area to a patient tray or being used for patient transport. This removes the leader from the simulated region and thus, a new leader has to be found.
Therefore, the vehicle the current leader belongs to should be assigned an occupation to prevent it being used for other purposes.