feat(GlSearchBoxByType): Add support for a borderless variant

mentioned in commit 6a3bed9b

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!116 (merged)

mentioned in merge request status-page!672 (merged)

mentioned in merge request gitlab!108150 (merged)

mentioned in merge request gitlab-docs!3416 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3204 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!117 (merged)