Add after_validation to ensure oid is updated

Kerri Millerrequested to merge
546678-add-before_validation-for-lfs_objects_projects.oid into master

What does this MR do and why?

We need to duplicate the oid information from lfs_objects to lfs_objects_project records. We've previously added the oid column (!192839 (merged)), and this MR will add an :after_validation to ensure that the value is copied over for new and updated records; this will ease our next step, backfilling the data.

Related to #546678 (closed)

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