Draft: Add support for GitLab Rails Nginx SSL

What does this MR do?

MR adds support to enable SSL for GitLab Rails Nginx. This is a core touchpoint and as a result the feature requires the following:

• Support for single node setups where external SSL variables are followed instead
• NGinx internal support (when behind load balancer with SSL termination)
• HAProxy CA support (when it is the load balancer with SSL termination)
• Gitaly Internal Callback Support (via Internal Load Balancer passthrough)

Related issues

Closes #446

Author's checklist

When ready for review, the Author applies the workflowready for review label and mention @gl-quality/get-maintainers:

• Merge request:
  • Corresponding Issue raised and reviewed by the GET maintainers team.
  • Merge Request Title and Description are up-to-date, accurate, and descriptive
  • MR targeting the appropriate branch
  • MR has a green pipeline
  • MR has no new security alerts in the widget from the Secret Detection and IaC Scan (SAST) jobs.
• Code:
  • Check the area changed works as expected. Consider testing it in different environment sizes (1k,3k,10k,etc.).
  • Documentation created/updated in the same MR.
  • If this MR adds an optional configuration - check that all permutations continue to work.
  • For Terraform changes: set up a previous version environment, then run a terraform plan with your new changes and ensure nothing will be destroyed. If anything will be destroyed and this can't be avoided please add a comment to the current MR.
• Create any follow-up issue(s) to support the new feature across other supported cloud providers or advanced configurations. Create 1 issue for each provider/configuration. Contact the Quality Enablement team if unsure.