Add a Let's Encrypt SSL cert renewal script and cronjob

[jhodapp]

Description

This PR adds a Let's Encrypt SSL cert renewal script, installs it into the deployment process, and sets up a cronjob to run this script twice a day.

GitHub Issue: N/A

Changes

• Adds a Let's Encrypt SSL cert renewal script called renew-cert.sh
• Adds it to deploy_to_do.yml deployment script to install on the DO droplet
• Adds a new cronjob to run this script every 12 hours

Testing Strategy

1. Test the deployment updates by changing the production env var BACKEND_IMAGE_NAME to ghcr.io/refactor-group/refactor-platform-rs/improve_lets_encrypt_ssl_cert_renewal:latest

2. Kick off a deployment from GitHub Actions making sure to deploy with the branch improve_lets_encrypt_ssl_cert_renewal

3. Test the renewal script in dry-run mode (won't actually renew, just checks):
   sudo certbot renew --webroot -w ./nginx/html --dry-run

4. If that works, test your actual renewal script:
   ./nginx/scripts/renew-certs.sh

5. Check that the log file was created:
   cat nginx/logs/letsencrypt-renewal.log

6. Verify nginx is still running and serving your site:

docker ps | grep nginx
curl -I https://refactor.engineer

7. Make sure to change the production env var BACKEND_IMAGE_NAME back to ghcr.io/refactor-group/refactor-platform-rs/main:latest

Concerns

None

[jhodapp]

Bypassing PR review rules since this is a timely fix to land and Claude gave a helpful an comprehensive PR review of with suggestions implemented.