Add edit to work item assignees

...ts/shared/work_item_sidebar_dropdown_widget_with_edit.vue

...ipts/work_items/components/work_item_assignees_inline.vue

...s/work_items/components/work_item_assignees_with_edit.vue

...ts/work_items/components/work_item_attributes_wrapper.vue

...s/work_items/components/work_item_milestone_with_edit.vue

...s/work_items/components/work_item_iteration_with_edit.vue

ee/spec/features/projects/work_items/okr_spec.rb

...rk_items/components/work_item_iteration_with_edit_spec.js

locale/gitlab.pot

spec/features/projects/work_items/work_item_spec.rb

...hared/work_item_sidebar_dropdown_widget_with_edit_spec.js

.../work_items/components/work_item_assignees_inline_spec.js

...rk_items/components/work_item_assignees_with_edit_spec.js

...ork_items/components/work_item_attributes_wrapper_spec.js

...rk_items/components/work_item_milestone_with_edit_spec.js

...rt/shared_examples/features/work_items_shared_examples.rb