Support for `expires_at` option in ActiveSupport::Cache::Store

Add expires_at to expire cache similar to expire_in


<% cache object, expires_at: object.created_at + 1.month do %>

<!-- something -->

<% end %>

I’m not sure if this is possible or if it breaks something else, but I can’t find it anything about this in the cache guides.

Thanks

Sounds good to me!