docs.rs: Forward If-None-Match header to origin so we can start returning 304

Author: syphar

terraform/docs-rs/cloudfront.tf

@@ -57,7 +57,7 @@ resource "aws_cloudfront_origin_request_policy" "docs_rs" {
   headers_config {
     header_behavior = "whitelist"
     headers {
-      items = ["User-Agent", "Referer"]
+      items = ["User-Agent", "Referer", "If-None-Match", "If-Modified-Since"]
     }
   }