Migrate to S3 bucket policy instead of access control

[Nadock]

The S3 bucket that stores the website contents defined in :/aws/website_cfn.yml uses the AccessControl: Private property, this is now considered a legacy property and "shouldn't be used".

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-s3-bucket.html#cfn-s3-bucket-accesscontrol

Migrating to a bucket policy is the solution, however it's not immediately clear what policy would correctly replace the old ACL configuration without breaking other things.