Redesign CI/CD linter to make it use new backend classes

The following discussion from gitlab-ce!13849 should be addressed:

• @grzesiek started a discussion:

  When might want to fix only/except representation here, it is currently refs, master, feature, kubernetes, configured which is confusing. I think we should create one additional tech debt issue for linter, because we have a pretty decent idea how to make linter to use CI config entries Entry#errors instead of attributes.