Ensure source timestamps are collected

[aiwilliams]

In order to support mechanisms such as dealing with an update operation that is reflecting an older state of source data, the integration SDK should work to ensure time stamps from the source are included in the entities/relationships.

The data model documents createdOn and updatedon for tracking the source timestamps. This should be required data, even if it is generated by the integration when it is not known/provided by the source, indicating the time that the integration collected the data, in case something else collects the data at a later time, but delivers it to the synchronizer earlier.

Once this data is ensured to be included in in the data delivered to the synchronization job, the persister should be able to rely it. It seems there is already some work it does to avoid overwriting newer data when an operation is stale.