Referrer-Policy should be updated

[csgrant83]

The Referrer-Policy is currently set to the default value of no-referrer-when-downgrade. I believe this should be something that can be set in the admin cp, so that an admin can chose to upgrade the policy. Right now if I use this plugin, I cannot update the policy short of turning off automatic rendering... which kind of defeats the point of this plugin from my point of view. For reference, I would like to be able to set the referrer policy to strict-origin-when-cross-origin.