Log TLS certificate renewals from Let's Encrypt

What does this MR do?

This merge request adds better logging of TLS certificate renewals completed through Let's Encrypt.

Related issues

Closes #3412 (closed)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks
• trigger-package has a green pipeline running against latest commit

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for the GitLab Chart opened

Testing

1. Install package with an https url in external_url that can successfully make a connection to Let's Encrypt
2. Set the cron job timings for auto-renewal to something about 5-6 minutes in the future in gitlab.rb
3. Watch the contents of /var/log/gitlab/lets-encrypt for the appropriate log

Closes #3412 (closed)