cloudfront: use CloudFront functions instead of Lambda

[mskrajnowski]

AWS introduced CloudFront functions which can replace viewer request/response Lambdas. They are simpler and cheaper, but with stricter time constraints. We should use them for basic auth for example.

https://aws.amazon.com/blogs/aws/introducing-cloudfront-functions-run-your-code-at-the-edge-with-low-latency-at-any-scale/
https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/cloudfront-functions.html