http: attach request as res.req

This change makes it possible for userland http-related modules
to pave over edge cases that require referencing the original request
when handling a response--making a "Lodash for HTTP" library possible.
More information and research in https://github.com/nodejs/node/issues/28673

Fixes: https://github.com/nodejs/node/issues/28673

PR-URL: https://github.com/nodejs/node/pull/36505


Reviewed-By: Robert Nagy <ronagy@icloud.com>