feature: upgrade to Yarn 2

Yarn 2 was released a year and a half ago, with the RC for Yarn 3 currently underway. The main benefits for me have been improvements to the `workspaces` feature, and the "zero node modules install" setup (where all your dependencies are zipped and committed into the repo)

https://yarnpkg.com/getting-started/qa#why-should-you-upgrade-to-yarn-modern

Wanted to check if there was interest before exploring whether that would be feasible in this repo.