【paddle.fleet】fleet add _get_applied_meta_list and _get_applied_graph_list, test=develop (#27952) (#28053)

* add doc; notest

* fix doc; notest

* update doc; notest

* refine optimizer && adam

* refine optimizer; notest

* add adam

* fix doc

* fix doc && add adamw; notest

* add error message

* bug fix

* refine rmsprop && adamax

* fix ci

* buf fix

* update comment

* unify arguments place; notest

* fix ut, test=develop

* bug fix

* fix conflicts, test=develop

* add examples code

* bug fix

* fix comments

* fix sample code

* add sample code for Optimizer

* add adamax ut, test=develop

* fix rmsprop ut, test=develop

* add ut for optimizer.py and adamw.py

* first commit of adadelta optimizer

* fix learning rate

* fix adadelta doc and add sgd momentum

* remove unused fluid

* fix codestyle

* Update test_adam_op.py

* Update test_adam_op.py

* fix SGD in 2 unittests

* fix SGD in 2 unittests

* fix ci

* fix ut
Co-authored-by: NMRXLT <xlt2024@gmail.com>
Co-authored-by: Nmapingshuo <mps2012@yeah.net>

* add save/load for parameter server

* add feature to fleet2.0 role_maker, distribute_strategy, test=develop

* move paddle.fleet to paddle.distributed.fleet

* add gradient Merge optimizer to meta, test=develop