E2E test for cloudflare/pp- components

This repository is part of a 4 component architecture
* [cloudflare/pp-origin](https://github.com/cloudflare/pp-origin),
* [cloudflare/pp-browser-extension](https://github.com/cloudflare/pp-browser-extension),
* [cloudflare/pp-attester](https://github.com/cloudflare/pp-attester),
* [cloudflare/pp-issuer](https://github.com/cloudflare/pp-issuer),

The current testing method relies on a dev environment to be deployed.

It would be good to automate it, and share this testbed across repos to validate individual changes. A sample test procedure could be:
* clone and start pp-issuer: `npm run dev -- --port 8787 && curl -X POST http://localhost:8787/admin/rotate`
* clone and start pp-attester: `npm run dev -- --port 8788 --var ISSUER_DIRECTORY_URL:"http://localhost:8787/.well-known/private-token-issuer-directory" --var ISSUER_REQUEST_URL:"http://localhost:8787/token-request"`
* clone and start pp-origin `npm run dev -- --port 8789 --var ISSUER_NAME:"localhost:8787" --var ORIGIN_NAME:"localhost:8789"`
* clone and build pp-browser-extension `npm run build`
* Start a Selenium session (in node.js), load the extension, updates options to have http://localhost:8788 as an attester, query the origin http://localhost:8789 with Javascript enabled (for client replay), confirm the success page is loaded.