Integrated Browser Performance Testing

What does this MR do?

Adds a section to the merge request widget that reports on performance metrics based on pipeline artifacts (similar to the security and codeclimate sections)

• add backend component that looks for jobs named "performance" or "deploy" with an artifact labeled "performance.json" and exposes the links to these artifacts to the MR widget
• add frontend component that accepts and parses these json files, and renders a section in the MR widget with the formatted data
• add tests
• create Auto DevOps template for a job that will produce these artifacts for a generic deployment

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan

What are the relevant issue numbers?

Closes #3046 (closed)