Draft: Heartbeat locking mechanism Duo Workflow Service

What does this merge request do and why?

1. Duo Workflow Side: !3515
2. Rails Side: gitlab-org/gitlab!207393
3. Issue: gitlab-org/gitlab#548686

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.
• If this change requires executor implementation: verified that issues/MRs exist for both Go executor and Node executor or confirmed that changes are backward-compatible and don't break existing executor functionality.