feat(GlBreadcrumb): Add `size` prop

mentioned in commit b8207f05

mentioned in merge request status-page!903

mentioned in merge request gitlab!180496 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!4289 (merged)

mentioned in merge request gitlab!181011 (closed)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!64 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!367 (merged)