Integration with Worker Sites

[jorgelbg]

Since a request can go through a single Cloudflare worker, it is not possible to run dashflare transparently. This is becoming more important after the release of Worker Sites that allow running a full website from the worker.

For this case, #7 introduced the possibility of forwarding the URL directly to the worker. This PR makes the worker stop behaving as a transparent proxy and just analyze the URL received via the x-original-url header.

Still pending:

• Document how to set up dashflare with a Worker Site
• Maybe publish a small npm module to do the forwarding
• Allow the possibility of forwarding also a status code, now it is hardcoded to 200
• Forwarding of the origin fetch time

See https://github.com/mre/endler.dev/blob/master/workers-site/index.js#L66-L73, is the only working example of this setup.