Adds LlamaForQuestionAnswering class in modeling_llama.py along with AutoModel Support (#28777)

* This is a test commit

* testing commit

* final commit with some changes

* Removed copy statement

* Fixed formatting issues

* Fixed error added past_key_values in the forward method

* Fixed a trailing whitespace. Damn the formatting rules are strict

* Added the copy statement

docs/source/en/model_doc/llama.md

@@ -116,6 +116,11 @@ A list of official Hugging Face and community (indicated by 🌎) resources to h
 [[autodoc]] LlamaForSequenceClassification
     - forward
 
+## LlamaForQuestionAnswering
+
+[[autodoc]] LlamaForQuestionAnswering
+    - forward
+
 ## FlaxLlamaModel
 
 [[autodoc]] FlaxLlamaModel