doc: add missing env variables to man page

This commit adds the missing environment variables
NODE_DEBUG_NATIVE, NODE_PRESERVE_SYMLINKS,
NODE_TLS_REJECT_UNAUTHORIZED, NODE_V8_COVERAGE, and
UV_THREADPOOL_SIZE to the man page.

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>