As a plugin writer, I can iterate over repository versions in a memory efficient manner
Plugins need to iterate over the content in a repository version to create a publication. Pulp
should offer a batching iterator over content in order to limit the memory footprint and to allow
efficient use of content batches in DB operations.
We could make
batch_qs() available to plugin writers. But this generator is hard to use correctly because of the ordering requirement (even in pulpcore it has not been used correctly).
Instead, add a generator to
RepositoryVersion, which does "the right thing" by default and is customizable by plugin writers if necessary.