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

The following discussion from !13849 (merged) 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.

changed title from Follow-up from "Check if Kubernetes is required when creating pipeline jobs" to Redesign CI/CD linter to make it use new backend classes

Although this is mostly technical debt it adds some value to customers because it would make GitLab CI/CD Linter much more verbose. /cc @bikebilly

added pipeline label

@bikebilly Let's say that this is a medium effort.