[feature] provide a possibility for the user application to read out the local DC time of the next Sync Event

Customer need to synchronize the application events with the DC time (i.e. diagnosis timestamp should be made using absolute DC time). The EtherCAT Slave itself synchronizes the Sync Events to the DC clock, the User Application is informed abot Sync Events too. But the User Application has no relation to the absolute value of the DC time.
The idea is to provide the local DC timestamp of the next (future) Sync Event in the DPM, so that the User Application can just read out the related timestamp after the Sync Event occured.