Follow-up from "feat(GlToken): use design tokens in GlToken"

The following discussion from gitlab-org/gitlab-ui!4578 (merged) should be addressed:

• @danmh started a discussion: (+2 comments)

  question: do we need another default in there? 😅

  color design token = token.default.foreground.color.default ?

task: when should we have a default at the end, and when not

task: update token system to follow this decision