* add: the contrastive search for generaton_utils
* add: testing scripts for contrastive search under examples/text-generation
* update the quality of codes
* revise the docstring; make the generation_contrastive_search.py scripts;
* revise the examples/pytorch/text-generation/run_generation_contrastive_search.py to the auto-APIs format
* revise the necessary documents
* fix: revise the docstring of generation_contrastive_search.py
* Fix the code indentation
* fix: revise the nits and examples in contrastive_search docstring.
* fix the copyright
* delete generation_contrastive_search.py
* revise the logic in contrastive_search
* update the intergration test and the docstring
* run the tests over
* add the slow decorate to the contrastive_search intergrate test
* add more test
* do the style, quality, consistency checks
