- Added a new method to return a list of errors instead of a single
  error string.
- Added simple join of structured error messages in Ci::LintsController
- Repeats some processing, but to avoid this would require refactoring
  exception raising and rescuing out of the entire class and all of its
  invocations across the application.
- Existing echnical debt issue addresses the overall problem:
  https://gitlab.com/gitlab-org/gitlab/issues/30066