We have this page in our documentation that explains how to generate Let's Encrypt certificates and configure our applications with them
Giving write permissions to other users to the configuration file of WordPress is not fully secure. Apache could modify that file and, in case it's hacked, someone could modify it and control the application.
If you want to use that plugin, you can modify its permissions by running this command
sudo chmod 664 /opt/bitnami/apps/wordpress/htdocs/wp-config.php
I hope this helps