Fixes #5526: Ensure content APIs are properly permission wrapped.

Intent is for packages, errata, package groups, and distributions the
user has :view_products and can then see the content for any products/repos
they have access to. For content within a content view, the user needs
:view_content_views permission.

For repository sets, a user needs :view_subscriptions to show, index or
see available repository sets and :import_manifest in order to disable/enable.