Global CDN Surrogate-Key-Raw Disabled by Default

The Surrogate-Key-Raw header, used for debugging when using Pantheon Advanced Page Cache, is no longer sent by default. To receive this header when making a request, send the Pantheon-Debug: 1 header, like so:

curl -IsH "Pantheon-Debug:1" https://example.com | grep key

This change addressed an issue that caused Twitter card validation to fail, and also reduces overall page size and speeds up page load time when sending many keys.