Support relative url on server side

[jim-king-2000]

Goals

Support relative url with fetch on server side

1. /abc
2. //domain.com/abc
3. ../abc

Non-Goals

No response

Background

We could use fetch('../abc') in the browser, but have to use fetch('https://domain.com/path') on server side. It makes code complicated.

Proposal

On the server side, we could get hostname and path (base url) of the request. Maybe we could provide some way to translate the relative path to the absolute path.