cli: add missing env vars to --help

This adds NODE_TLS_REJECT_UNAUTHORIZED, SSL_CERT_DIR,
SSL_CERT_FILE, and UV_THREADPOOL_SIZE to the --help menu.

PR-URL: https://github.com/nodejs/node/pull/24383


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ouyang Yadong <oyydoibh@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>