During a project import, `LfsLinkService` attempts to link `LfsObjects`
that have not already been associated with a project.  It's possible for
a large repo to have thousands of OIDs, which can cause long database
query and parsing times.  By processing a batch of 1000 at a time, we
can reduce that time at the expense of a few more SQL queries.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/66274