Add optional middleware for removing `Set-Cookie`

* In my case, Clearance middleware was adding `Set-Cookie` to every request
* This occured after `set_cache_control_headers` was called, whether it was a
  `before_filter` or `after_filter`
* Optional middleware looks for `Surrogate-Control` header so it only removes
  `Set-Cookie` for endpoints not being cached by Fastly
How about adding `Surrogate-Key` also. These jump out to me as the two main Fastly use cases.

```ruby
if headers["Surrogate-Control"] || headers["Surrogate-Key"]
```