[Feature] Add support for React SSR apps

[andrewgadziksonos]

Looking for support to add Remix or NextJS support into EdgeWorkers. Some of the missing features that are needed are described here,

https://github.com/remix-run/remix/issues/1539

TL;DR

• Add body to the request object used in onClientRequest and onOriginRequest in order to support POST requests

OR

• Add support for other HTTP methods for responseProvider

IMHO, the second option feels like the more appropriate spot to handle application requests