* test=develop, util documents

* test=develop, add ps auto

* fix heter-ps multi thread

* fix fluid.embedding

* Support Heter Parameter Server

* fix decay global counter

* remove unused print, test=distp0

* support ps-gpu

* move paddle.fleet to paddle.distributed.fleet

* fix merge3 test=develop

* fix large scale KV 
* fix single training using async ssa graph

* test=develop,test=document_fix, remove the out args

* fleet_util move to paddle.fleet
Co-authored-by: NWuHaobo <wuhaobo1994@gmail.com>
Co-authored-by: Ntangwei12 <tangwei12@baidu.com>

* add heter ps mode

* code style
test=develop

* add with_pslib
test=develop

* unitest
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* code style
test=develop

* test monitor
test=develop

* prepare trainer
test=develop

* code style
test=develop

Integrated Trainer of Parameter Server (API add `fluid.contrib.layers.sparse_embedding` only) (#22957)

* Integrated Trainer of Parameter Server

* add mock barrier all
test=develop

* fix
test=develop

* fix
test=develop

* fix
test=develop

* add timeout and http store in communication, add revert and confirm in fleet
* test=develop

* allow amp and recompute working together

* fix judge pslib & ranspiler

* add unit accessor in fleet, support DownpourUnitAccessor
* test=develop

* fix add dense table
test=develop

* fix
test=develop

* fix
test=develop

* add save with prefix
* test=develop

* add fleet pslib pull and push sparse op and push dense op
* test=develop

* fix no cvm, when accessor is DownpourSparseValueAccessor, set no_cvm=True
* test=develop

* add clear_one_table
* test=develop

This reverts commit 66fce9e8.

Fleet Parameter Server API Integrated

* fix add grad bug test=develop

* update style test=develop

* test=develop, optimize distributedstrategy

* add sync communicator and implement