[All models] Extend config.output_attentions with output_attentions function arguments (#4538)
* DOC: Replace instances of ``config.output_attentions`` with function argument ``output_attentions``
* DOC: Apply Black Formatting
* Fix errors where output_attentions was undefined
* Remove output_attentions in classes per review
* Fix regressions on tests having `output_attention`
* Fix further regressions in tests relating to `output_attentions`
Ensure proper propagation of `output_attentions` as a function parameter
to all model subclasses
* Fix more regressions in `test_output_attentions`
* Fix issues with BertEncoder
* Rename related variables to `output_attentions`
* fix pytorch tests
* fix bert and gpt2 tf
* Fix most TF tests for `test_output_attentions`
* Fix linter errors and more TF tests
* fix conflicts
* DOC: Apply Black Formatting
* Fix errors where output_attentions was undefined
* Remove output_attentions in classes per review
* Fix regressions on tests having `output_attention`
* fix conflicts
* fix conflicts
* fix conflicts
* fix conflicts
* fix pytorch tests
* fix conflicts
* fix conflicts
* Fix linter errors and more TF tests
* fix tf tests
* make style
* fix isort
* improve output_attentions
* improve tensorflow
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>