chore: migrate component examples from GitLab UI

This migrates all GitLab UI examples into design.gitlab.com, as described in gitlab-org/gitlab-ui#978 (closed)

Since this moves a lot of files at once and might not be easy to review, here's a script to replicate the migration: https://gitlab.com/pgascouvaillancourt/migrate-gitlab-ui-examples

Note that after running the script, yarn lint:fix must be run in design.gitlab.com to produce consistent results with this MR.