Fixes #7059 - enable pagination in subscriptions (API)

These are already included here:  https://github.com/Katello/katello/blob/master/app/controllers/katello/api/v2/api_controller.rb#L36

I believe the subscriptions controller index should work if do this`/katello/api/v2/organizations/1/subscriptions?page=4&per_page=3`

If you want the entire result you can pass in `full_result=true`.