[gpt-neox] Add attention_bias config to support model trained without attention biases
Author: dalgarak
Pull request: yes

# What does this PR do?

This PR adds attention_bias configuration into GPT-NeoX models. Currently released models all use bias by default for the linear layers in attention block, but the GPT-NeoX library allows us to train models without attention bias. (can be trained with use_bias_in_attn_linear=False)

For compatibility with existing models, we set the default value of attention-bias to True. I've done some testing and verified the behavior with attn_implementation="flash_attention_2".

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Comments:
cc @ArthurZucker @younesbelkada 

Best of my knowledge, there are many(and almost) gpt-neox models are on the hub that uses attention bias:
 * pythia scailing suite family, e.g. EleutherAI/pythia-70m (https://huggingface.co/EleutherAI/pythia-70m),
 * polyglot korean LMs, e.g. EleutherAI/polyglot-ko-1.3b (https://huggingface.co/EleutherAI/polyglot-ko-1.3b)
 * and gpt-neox models, e.g. EleutherAI/gpt-neox-20b

and not public released yet(because training is undergoing)- but we want to release a model to hub, which trained GPT-NeoX architecture **without** attention bias. 

To check attention_bias=False configure, we upload a 'intermediate checkpoint' of model of ours to the hub; see https://huggingface.co/dalgarak/gnx_6.7b_no_attn_bias_test 
(NOTE: public, gated user access but will approve automatically. it will available until this-or related PRs- closed.)



The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_28126). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

oh, I found a mistake in argument documentation, fixed it now. Thanks!