Migrate work_item_weight.vue to use WorkItemSidebarWidget

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/184194



Merged-by: Coung Ngo <cngo@gitlab.com>
Approved-by: Cindy Halim <chalim@gitlab.com>
Approved-by: Florie Guibert <fguibert@gitlab.com>
Reviewed-by: Coung Ngo <cngo@gitlab.com>