http: increase default header size from 8KB to 16KB

Fixes: https://github.com/nodejs/node/issues/27645

PR-URL: https://github.com/nodejs/node/pull/32520


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>