Added Cloudfront custom error responses

[bendubuisson]

CloudFront custom error responses like so:

module "static-website" {
[...]
  cloudfront_custom_error_responses = [
    {
      error_caching_min_ttl = 10
      error_code            = 404
      response_code         = 404
      response_page_path    = "/404.html"
    },
    {
      error_caching_min_ttl = 10
      error_code            = 403
      response_code         = 404
      response_page_path    = "/404.html"
    },
  ]

}