Ads: inject ads below posts loaded via Infinite Scroll as well

> I noticed an ad tacked on to my first post on the blog listing. But, if I scroll and trigger more posts through infinite scroll, I don’t notice any more ads. Should we be showing ads on the 2nd, 3rd, etc. pages as well? Maybe make this customizable?

No file, test, or entry point is named. Start by tracing how ads are added to the initial blog listing and how infinite-scroll posts are loaded; done would mean deciding and documenting whether subsequent pages receive ads and whether that behavior is customizable.

Written by the indexing model from the issue text.