Refactor `work_item_parent` widget to use `work_item_sidebar_dropdown_widget`

work_item_parent widget should be refactored to use work_item_sidebar_dropdown_widget for uniformity and scalability

When working on Resolve "Use apollo resolver for fetch/update n... (!151889 - merged), to fetch the parent selected in the dropdown I had to dig in the the code on the implementation vs checking the known props and implementation of dropdowns in the work item sidebar.

Right now , 5 dropdown widgets(assignees, labels, milestone, iteration and health status) use the reusable wrapper vs the parent widget not using the same. Having the same component makes sure that there is uniformity in implementation and any fix or change in implementation applies to all.

For example, this issue of forcing all the dropdowns to up will be fixed for all the widgets using the component rather than just the parent widget.

Hence this should be done , but not too important for %17.1 , we can also plan it for next milestone