accelerate deepspeed and gradient accumulation integrate
### What does this PR do?
1. Shift deepspeed integration to accelerate
2. Shift Gradient Accumulation to Accelerate
3. Merge after #23168 
4. no user facing change. Now user can use `accelerate launch` with trainer for DeepSpeed, e.g.:
```
accelerate launch --num_processes=2 --mixed_precision=bf16 --use_deepspeed --gradient_accumulation_steps=1 --gradient_clipping=1 --zero3_init_flag=True --zero3_save_16bit_model=False --zero_stage=3 --offload_optimizer_device=none --offload_param_device=none ./examples/pytorch/text-classification/run_glue.py  --model_name_or_path bert-base-cased   --task_name $TASK_NAME   --do_train   --do_eval   --max_seq_length 128   --per_device_train_batch_size 16   --learning_rate 5e-5   --num_train_epochs 3   --output_dir /tmp/$TASK_NAME/ --overwrite_output_dir --bf16
```

Usual run using `torchrun` and trainer args is unimpacted:
```
torchrun --nnodes 1 --nproc-per-node 2 ./examples/pytorch/text-classification/run_glue.py  --model_name_or_path bert-base-cased   --task_name $TASK_NAME   --do_train   --do_eval   --max_seq_length 128   --per_device_train_batch_size 16   --learning_rate 5e-5   --num_train_epochs 3   --output_dir /tmp/$TASK_NAME/ --overwrite_output_dir --deepspeed ~/transformers/tests/deepspeed/ds_config_zero2.json
```
5. Save and load utils are changed accordingly
_The documentation is not available anymore as the PR was closed or merged._<|||||>> Thanks for working on this. Is the diff longer than expected because of other PRs to be merged before?

Due to updating from main, it is not showing the diff wrt previous branches. Weird. 

> Might be cool to Have Stas have a look (not pinging him here too early) once this is ready to merge and tests are confirmed to all pass.

Yes, definitely. All tests are passing already. Checked the slow tests offline.
<|||||>@sgugger, now the diff is only specific to DeepSpeed changes + gradient accumulation changes + saving/loading changes wrt previous PR.<|||||>Hello @stas00, please review this PR which aims to shift the accelerate handling in Trainer to Accelerate. Thank you!