Merge branch 'tbulva-work-item-subitems' into 'master'

Work item - sub items - part 2

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/171956



Merged-by: Deepika Guliani <dguliani@gitlab.com>
Approved-by: Martin Čavoj <mcavoj@gitlab.com>
Approved-by: Missy Davies <mdavies@gitlab.com>
Approved-by: Deepika Guliani <dguliani@gitlab.com>
Reviewed-by: Dmitry Gruzd <dgruzd@gitlab.com>
Reviewed-by: Mireya Andres <mandres@gitlab.com>
Reviewed-by: Martin Čavoj <mcavoj@gitlab.com>
Reviewed-by: Missy Davies <mdavies@gitlab.com>
Co-authored-by: Mireya Andres <mandres@gitlab.com>
Co-authored-by: Tomas Bulva <tbulva@gitlab.com>