GitLab

* add lambdarank for cuda_exp

* support unlimited number of ranks in labels

* fix lint errors

* remove warning for lambdarank with cuda_exp

* Update src/objective/cuda/cuda_rank_objective.hpp
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* Update src/objective/cuda/cuda_rank_objective.hpp
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>