Update design.GitLab.com with new brand assets

Problem to solve

Update to design.GitLab.com which with the pajamas logo (and pattern if appropriate)

Further details

Relies on https://gitlab.com/gitlab-org/design.gitlab.com/issues/88

Proposal

Something similar to https://design.trello.com/

What does success look like, and how can we measure that?

• Design.GitLab.com landing page is updated with pajamas logo (and pattern if appropriate)

Links / references