UI: Display information about sign-offs

[flosell]

Manual triggers are often used as sign-offs, e.g. before a critical deployment. Similar to #159, we could display this information if metadata following a particular convention is followed, e.g.

• on the build step sign off by John Doe
• a list of signoffs:
  • stage QA signoff by John Doe
  • stage PROD signoff by John Doe