Create a background migration to populate lfs_objects_projects

As part of the sharding/cells/org mover work, we have been directed:

lfs_objects_projects: we add lfs_objects_projects.oid as a way to OrgMover/migration to recover Oid relation

The first step is to create an oid column on lfs_projects_objects. Once that is complete, we can create a background migration to copy oid from lfs_objects.oid to lfs_objects_projects.oid