Add linter rule to prevent self-referential module imports

Why

We’ve found several self-referential statements in gitlab-ui. By self-referential, I mean import { GlIcon, GlNewButton } from '@gitlab/ui'; statements in files that belong to @gitlab/ui.

These statements cause problems for gitlab-ui clients trying to mock a subset of gitlab-ui using jest manual mocks.

More info in: gitlab-org/gitlab-ui!958 (merged)