Deprecated use of `ForwardedValues` in "Bref for Web Apps"

[afu-dev]

Just discovered when checking the documentation of ForwardedValues that this field has been deprecated: https://docs.aws.amazon.com/cloudfront/latest/APIReference/API_ForwardedValues.html

It's currently used in some place like https://github.com/brefphp/bref/blob/master/docs/websites.md (https://bref.sh/docs/websites.html).

We should be using CachePolicy now (AWS::CloudFront::CachePolicy).