Manage project labels from sidebar in graphql-based project boards

In graphql-based project boards (requires :graphql_board_lists), the label select dropdown doesn't have the feature to add a new project label.

The feature spec to test this behavior will be skipped for now after !56458 (merged) merges.

• spec/features/boards/sub_group_project_spec.rb

classic project boards	graphql-based project boards