GPTNeoForQuestionAnswering (#23057)

* first draft - gives index error in question_answering.py

* maturing

* no labels

* pipeline should know about QA

* fixing checks

* formatting

* fixed docstring

* initial commit

* formatting

* adding the class to many places

* towards less unhappy checks

* nearly there

* Update src/transformers/models/gpt_neo/modeling_gpt_neo.py

Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* avoid error

* moving to device of star/end_logits

---------

Co-authored-by: Prof. Peter Schneider-Kamp <jps@ordbogen.com>
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

docs/source/en/model_doc/gpt_neo.mdx

@@ -69,6 +69,11 @@ The `generate()` method can be used to generate text using GPT Neo model.
 [[autodoc]] GPTNeoForCausalLM
     - forward
 
+## GPTNeoForQuestionAnswering
+
+[[autodoc]] GPTNeoForQuestionAnswering
+    - forward
+
 ## GPTNeoForSequenceClassification
 
 [[autodoc]] GPTNeoForSequenceClassification