Performance: Pre-compress and serve Brotli assets

Created by: umpox

Some stats:

• Our biggest bundles are reduced in size by around 25%. This is great because these bundles are typically the ones we load on every page. For example, our main app.bundle.js file is reduced from 749kb to 555kb!
• Average size reduction of ~18% for all files above 50kb
• Average size reduction of ~15% for all files above 10kb

All browsers we target should support Brotli, we fallback to standard .js files which we dynamically compress with gzip on the server anyway.

Required update to our assets server: https://github.com/sourcegraph/httpgzip/pull/1/files

Before

After