Collection cache max age should be 5m

www.agileplannerapp.com/boards/173808/cards/8023

HMRC need to publish a collection page which needs to reflect the latest changes in no longer than 5m.

made a change to the `CacheControlHelper` to allow overriding the `cache_max_age` from the controller, so that we can set a max age of 5m for collections.
I was trying to keep all configurables in one place. We could move it to the controller instead, but then `uploads_cache_max_age` should also be moved to the respective controller. What do you suggest?