[Feature] Support ReduceOnPlateauParamScheduler(#819)

* [Feature] Add ReduceOnPlateauParamScheduler and change ParamSchedulerHook

* [Feature] add ReduceOnPlateauLR and ReduceOnPlateauMomentum

* pre-commit check

* add a little docs

* change position

* fix the conflict between isort and yapf

* fix ParamSchedulerHook after_val_epoch execute without train_loop and param_schedulers built

* Apply suggestions from code review

Co-authored-by: Mashiro <57566630+HAOCHENYE@users.noreply.github.com>

* update ReduceOnPlateauParamScheduler, ReduceOnPlateauMomentum and ParamSchedulerHook

* fix get need_step_args attribute error in ParamSchedulerHook

* fix load_state_dict error for rule in ReduceOnPlateauParamScheduler

* add docs for ParamSchedulerHook and fix a few codes

* [Docs] add ReduceOnPlateauParamScheduler, ReduceOnPlateauMomentum and ReduceOnPlateauLR docs

* [Refactor] adjust the order of import

* [Fix] add init check for threshold in ReduceOnPlateauParamScheduler

* [Test] add test for ReduceOnPlateauParamScheduler, ReduceOnPlateauLR and ReduceOnPlateauMomentum

* [Fix] fix no attribute self.min_value

* [Fix] fix numerical problem in tests

* [Fix] fix error in tests

* [Fix] fix ignore first param in tests

* [Fix] fix bug in tests

* [Fix] fix bug in tests

* [Fix] fix bug in tests

* [Fix] increase coverage

* [Fix] fix count self._global_step bug and docs

* [Fix] fix tests

* [Fix] modified ParamSchedulerHook test

* Update mmengine/optim/scheduler/param_scheduler.py

Co-authored-by: Mashiro <57566630+HAOCHENYE@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Mashiro <57566630+HAOCHENYE@users.noreply.github.com>

* [Fix] modified something according to commented

* [Docs] add api for en and zh_cn

* [Fix] fix bug in test_param_scheduler_hook.py

* [Test] support more complicated test modes(less, greater, rel, abs) for ReduceOnPlateauParamScheduler

* [Docs] add docs for rule

* [Fix] fix pop from empty list bug in test

* [Fix] fix check param_schedulers is not built bug

* [Fix] fix step_args bug and without runner._train_loop bug

* [Fix] fix step_args bug and without runner._train_loop bug

* [Fix] fix scheduler type bug

* [Test] rename step_args to step_kwargs

* [Fix] remove redundancy check

* [Test] remove redundancy check

* Apply suggestions from code review

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* [Test] fix some defects

Co-authored-by: Mashiro <57566630+HAOCHENYE@users.noreply.github.com>
Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>