[PROPOSAL] purl type `jsr`

[jkowalleck]

The JavaScript Registry (JSR) is a modern package registry for JavaScript and TypeScript. JSR works with many runtimes (Node.js, Deno, Bun, browsers, and more) and is backwards compatible with npm. Learn more about why we built JSR.
-- https://jsr.io/docs/introduction

JSR is (going to be) a first citizen in

• deno's package manager - since v1.42 (https://deno.com/blog/v1.42)
• yarn package manager - since v4.9 (https://github.com/yarnpkg/berry/releases/tag/%40yarnpkg/cli/4.9.0)
• pnpm package manager - upcoming (via Add support for installing JSR packages directly pnpm/pnpm#8941)
• ... TBC ...

Some site notes: JSR is not a mirror of https://www.npmjs.com/. they are an independent package registry (even though they provide a npm-compatible API) - they might focus on a whole different type of packages, distribution, and so on ...

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I'd propose a custom purl type for JSR.

this ticket solves parts of #302