When `options.path` passed to `http.request()` contains an absolute
URL, `http.request` has been sending it directly as the request target
in the HTTP 1.1 message. If the receiving server is a proxy,
the proxy server typically forwards the request to the destination
specified in the request target and ignores the Host header.
This means eventually the request can be forwarded to a destination
that is not consistent with `options.host`, depending on how the
receiving server behaves. Mimatched Host header and request target
also violates RFC 9112 Section 3.2, which we have been entirely
leaving to the users to verify.

This patch documents this behavior and warns that the user needs
to ensure the `path`, `option` and `headers` conform to the RFC.
If the receiving server is known to be a proxy server because
the request is routed by Node.js' built-in HTTP proxy support,
we now do a best-effort check to verify that the authority in
`options.path` (if absolute), Host headers and `options.host`
agree at request construction time. Node.js will give up on the
require target rewriting and throw an error when they don't match
at request construction.

Signed-off-by: Joyee Cheung <joyeec9h3@gmail.com>