Converting TTF/OTF to WOFF2

**Feature request summary**

there should be an audit advising the usage of modern font formats

i could potentially work on it

**What is the motivation or use case for changing this?**
it seems like an obvious recommendation since we already advise usage of avif/webp

Start with docs/new-audits.md, then trace how existing AVIF and WebP recommendations are implemented and tested. The work is complete when Lighthouse has an audit that identifies TTF/OTF usage and advises a modern WOFF2 font format.

Written by the indexing model from the issue text.