Lower the Price Class for each distribution

There are three price classes available to choose from described on the
AWS CloudFront documentation located here:

https://aws.amazon.com/cloudfront/pricing/

We have came to the conclusion, that we can safely set the class, to the
smallest and cheapest one, covering only US, CA and EU as we don't think
these will be accessed from outside of EU. Although still accessible, it
will take longer, to locate the nearest CDN server, to the country
outside of our scope.

terraform/cloudfront/cloudfront_distribution/distribution.tf

@@ -45,6 +45,8 @@ resource "aws_cloudfront_distribution" "cdn_instance" {
     max_ttl                = 86400
   }
 
+  price_class = "PriceClass_100"
+
   restrictions {
     geo_restriction {
       restriction_type = "none"