feat: add yarn

[nickajacks1]

Yarn is a bit unique in that it recommends installing via Corepack. To facilitate adding yarn via hermit, we can take the same approach that the official Node.JS Docker image takes, which is to install yarn v1, which can then be used to bootstrap yarn v2 and higher.

Provides an alternative to Corepack for those using Yarn. See also: #253
Validated against a yarn v3 project using the pnp linker.

[alecthomas]

Hermit generally doesn't get involved in installing language specific packages. For example, the recommended means of installing yarn is via npm.

[nickajacks1]

You are right that you can install it using npm. I incorrectly remembered there being a warning that you are not supposed to use install yarn from an npm install...maybe I confused that with apt or something. Anyway, I suppose I see yarn a bit more like pnpm (which is provided by hermit) as being its own package manager rather than an npm package itself.

By following what the official Node Docker image does and installing the "binary" release of yarn, Hermit would let my team run yarn right away without having to remember to run npm install --global yarn or corepack enable for each cloned repo. In my opinion that leads to a much nicer and transparent experience.

That is just my opinion. If you disagree, please close this at your discretion.

[nickajacks1]

Thought about it some more, and given the uncertainty of the future of corepack and how nodejs package managers will be installed, it probably makes sense to at the very least hold off on this.
yarnpkg/berry#6443