Cache featured collections, as well as outbox, followers and following

[ClearlyClaire]

No description provided.

[ClearlyClaire]

When a status is suddenly boosted or replied out of the usual audience of an account, many instances may try to resolve that account at the same time, fetching various collections (outbox, followers, following, featuring). While the first ones are usually just a “wrapper” with just the number of items and a link to the first page, and are thus rather cheap, it doesn't hurt to let the reverse-proxy handle them. The featured collection is potentially more expensive, caching it both on the reverse-proxy and at the Rails level makes sense.