Hierarchy widget - add parent/child widget when showing a work item

add a new grapqhl type for exposing parent/child data (e.g. !85700 (diffs))
expose permissioned list child items through this widget and also parent item, ordered by relative position (relative positioning is not included in POC). Ordering by relative_position doesn't have to be part of MVC (#358195 (comment 932035936))
hierarchy widget should be developed behind a feature flag

Edited May 19, 2022 by Seth Berger