Currently, rolling CVs are hard coded to use the Library environment at all times.

We received user feedback that this limitation is especially painful considering smart proxy syncs, because it forces users to sync all of library to smart proxy in order to use any rolling CVs.

Another potential use case is to register a host linked to both a normal and a rolling content view (but in a non-Library environment used by the normal content view).

This feature has received a lot of discussion here: https://community.theforeman.org/t/transparent-content-view-for-limiting-repository-access-in-katello/39389/33

After much back and forth we decided to implement the maximally flexible solution of allowing rolling CVs to be associated with arbitrary sets of library environments.

Adding/removing environments from rolling CVs bypasses the "publish" workflow used by regular content views, and is instead done as part of the "Update" action.

When new content is synced to library, all "rolling repo clone" repos in all environments are immediately updated as part of the sync (and smart proxy syncs are scheduled as appropriate).