Implement `failure_reason` on `ci_builds`

What does this MR do?

This MR implements failure_reason on ci_builds.

Are there points in the code the reviewer needs to double check?

Is this useful?

Why was this MR needed?

Required for finishing https://gitlab.com/gitlab-org/gitlab-ce/issues/34834

Screenshots (if relevant)

N/A

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [-] Documentation created/updated
• API support added
• 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

What are the relevant issue numbers?

• Related : https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/2722#note_39166760
• Close https://gitlab.com/gitlab-org/gitlab-ce/issues/37239

/cc @ayufan @godfat