test: improve https_renew_cert.sh script - #42343

- To avoid unnecessarily large diffs, only generate a new private key
  if necessary. Otherwise, reuse the existing private key and only
  issue a new certificate.
- Remove an unnecessary conversion step using openssl rsa and the
  intermediate rsa.pem and csr.pem files.
- Extend the certificate validity from 1 year to 10 years.
- Show a text representation of the issued certificate upon completion
  such that the user can verify the validity.
- Make the script executable.
- Use "#!/usr/bin/env bash" instead of "#!/bin/bash".
- Allow the script to be called from any directory.

Refs: nodejs#42342
Refs: nodejs#37990