Add better assets compression to CE

[ruslandoga]

Changes

This PR enables static assets compression in CE. And additionally adds a library with better Gzip and Brotli defaults.

Relevant card: https://3.basecamp.com/5308029/buckets/29267832/card_tables/cards/7559344001

Right now CE sends static assets uncompressed (unless the reverse proxy compresses them).

https://github.com/hauleth/phoenix_bakery digests statis assets (on mix phx.digest) to (better compressed) gzip and also brotli so that Plug.Static :gzip and :brotli options could be set to true which would make it serve well compressed static assets. This would be useful once we start removing reverse-proxies from the default CE setup.

Tests

• [x] This PR does not require tests

Changelog

• [x] Entry has been added to changelog

Documentation

• [x] This change does not need a documentation update

Dark mode

• [x] This PR does not change the UI