http: add maxHeaderSize property

This commit exposes the value of --max-http-header-size
as a property of the http module.

Backport-PR-URL: https://github.com/nodejs/node/pull/25218
PR-URL: https://github.com/nodejs/node/pull/24860


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>