doc.rust-lang.org: add caching headers for static content

[jsha]

Steps to reproduce:

1. Load any doc.rust-lang.org page, e.g. https://doc.rust-lang.org/std/str/index.html.
2. Open Developer Console.
3. Click the URL bar and hit enter to load the page again.

Expected result:

Most resources are cached and do not hit the network.

Actual result:

Many objects require a network fetch, but get a 304 Not Modified. These should be served with long caching headers.

Current headers:

$ curl -I https://doc.rust-lang.org/SourceCodePro-Regular.woff
HTTP/2 200 
content-type: font/woff
content-length: 55472
last-modified: Thu, 11 Feb 2021 14:27:46 GMT
x-amz-version-id: R.xOjlR7eKEsQwzm9EIrHs9eeCIDeXYq
server: AmazonS3
date: Thu, 18 Feb 2021 13:27:31 GMT
etag: "957fa8c030f8116bea59c13df470e4e8"
x-cache: Hit from cloudfront
via: 1.1 4b84530d7a095b58fb7a1d20b7f0cbe0.cloudfront.net (CloudFront)
x-amz-cf-pop: HIO50-C2
x-amz-cf-id: QpMYsW6BVcTPpDmi8Pg9HiMz_1iSOIpdYv60MMzNqVoV707yqsv_Dw==
age: 63023

[jsha]

Adding a separate topic here because it's closely related: We can achieve a significant decrease in file size by enabling Brotli compression, which is an option in CloudFront: https://aws.amazon.com/about-aws/whats-new/2020/09/cloudfront-brotli-compression/

Brotli has been supported in major browsers since 2016: https://en.wikipedia.org/wiki/Brotli

search-index1.50.0.js is currently served as 272,247 gzip bytes, but it could be served as 140,170 brotli bytes.

$ curl https://doc.rust-lang.org/search-index1.50.0.js --header "Accept-Encoding: gzip" -o search-index.js.gz
$ zcat search-index.js.gz | brotli > search-index.js.br
$ ls -l search-index.js.*
-rw-rw-r-- 1 jsha jsha 140170 Feb 18 23:56 search-index.js.br
-rw-rw-r-- 1 jsha jsha 272247 Feb 18 23:56 search-index.js.gz

[tesuji]

Brotli has been supported in major browsers since 2016: https://en.wikipedia.org/wiki/Brotli

Per https://caniuse.com/brotli, IE browser doesn't support this header. But since it's just a header, I don't think any incompatibility problems here with IE. However, changing the header shall be done by rust-infra/docs.rs team, not rustdoc it self as rustdoc have to serve pages from local files.

[jsha]

Opened issues on rust-lang/simpleinfra instead, so closing this. Thanks for the guidance!