Allow addons with only unlisted versions to be linked externally on Primary Hero shelf #6832
Description
From #6813
It should also be possible to feature unlisted Recommended extensions in the homepage (and we most likely will at launch). The Call to Action will point to the homepage URL, so having one set should be another requirement to enable the checkbox in the admin, for unlisted ones.
Filing separately because it's a follow on from #6819 - but makes the issue more complicated.