Description of problem:

Content views which have moved from IMMEDIATE to ON_DEMAND download policy in the active library environment are excluded from diff calculations in incremental exports. This content is snapshotted and archived in the complete export, so it should be available in the incremental export as well.

How reproducible:

Always

Is this issue a regression from an earlier version:

No

Steps to Reproduce:

1. Create a repository with IMMEDIATE download policy and sync it.
2. Add the repository to a content view and publish v1.
3. Complete export the CV: `hammer content-export complete version --organization <org> --content-view <cv> --version "1.0"`.
4. Modify the library repository's download policy to ON_DEMAND, add a small package for diff purposes, and publish v2.
5. Get the `history-id` of the complete export: `hammer content-export list --organization <org> --content-view <cv>`
6. Run an incremental export on the complete export: `hammer content-export incremental version --organization <org> --content-view <cv> --version "2.0 --from-history-id <id>"

Actual behavior:
`app/services/katello/pulp3/content_view_version/export.rb:54`'s `immediate_or_none` filters on the library content view's current download policy, causing content that was included in the complete content export to be filtered out of diff calculations for the incremental export. Incremental export fails with `undefined method `output_file_info' for nil:NilClass`.

Expected behavior:
All repositories in the previous content view version snapshot (v1) should be included in the incremental export's diff calculations. The incremental export should succeed and include the small test package added in the content view version 2.

Business Impact / Additional info:

I have a theory that this behavior was unearthed after we fixed some of the `--from-history-id` issues with incremental export. Many airgapped customers rely on these incremental exports being rock-solid; this should be a priority to fix.