Add CodeGen model (#17443)

* Add CodeGen model

* Add missing key and switch order of super()

* Fix torch.ones init with uint8 instead of bool

* Address comments: copy statements and doc

* update tests

* remove old model parallel

* fix batch gen tests

* fix batch gen test

* update test_gpt2_sample_max_time

* fix codgen test and revert gpt2 test change

* Fix incorrect tie_word_embedding value, typo, URL

* Fix model order in README and styling

* Reorder model list alphabetically

* Set tie_word_embedding to False by default

* Apply suggestions from code review

* Better attn mask name & remove attn masked_bias

* add tokenizer for codegen

* quality

* doc tokenizer

* fix-copies

* add CodeGenTokenizer in converter

* make truncation optional

* add test for truncation

* add copyright

* fix-copies

* fix fast tokenizer decode

* Update src/transformers/models/codegen/tokenization_codegen.py

Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

* increase vocab_size in tests

Co-authored-by: patil-suraj <surajp815@gmail.com>
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

docs/source/en/serialization.mdx

@@ -54,6 +54,7 @@ Ready-made configurations include the following architectures:
 - Blenderbot
 - BlenderbotSmall
 - CamemBERT
+- CodeGen
 - ConvBERT
 - ConvNeXT
 - Data2VecText