Add verification status widget for requirements

app/assets/javascripts/graphql_shared/possible_types.json

app/graphql/resolvers/work_items_resolver.rb

doc/api/graphql/reference/index.md

ee/app/graphql/ee/resolvers/work_items_resolver.rb

ee/app/graphql/ee/types/work_items/widget_interface.rb

...phql/types/work_items/widgets/verification_status_type.rb

ee/app/models/ee/work_item.rb

ee/app/models/ee/work_items/type.rb

ee/app/models/work_items/widgets/verification_status.rb

ee/spec/factories/work_items.rb

ee/spec/graphql/types/work_items/widget_interface_spec.rb

...types/work_items/widgets/verification_status_type_spec.rb

ee/spec/models/ee/work_items/type_spec.rb

ee/spec/models/work_item_spec.rb

...pec/models/work_items/widgets/verification_status_spec.rb

ee/spec/requests/api/graphql/project/work_items_spec.rb

ee/spec/requests/api/graphql/work_item_spec.rb