Adding OPTForSeqClassification class (#18123)

* Adding OPTForSeqClassification class

* Fix import issues

* Add documentation for optforseqclassification

* Remove checkout

* fix failing tests

* fix typo

* Fix code formatting

* Incorporating the PR feedbacks

* Incorporate PR Feedbacks

* Fix failing test and add new test for multi label setup

* Fix formatting issue

* Fix failing tests

* Fix formatting issues

* Fix failing tests

* Fix failing tests

* Fix failing tests

* Fix failing tests

* PR feedback

docs/source/en/model_doc/opt.mdx

@@ -54,6 +54,11 @@ The original code can be found [here](https://github.com/facebookresearch/metase
 [[autodoc]] TFOPTForCausalLM
     - call
 
+## OPTForSequenceClassification
+
+[[autodoc]] OPTForSequenceClassification
+    - forward
+
 ## FlaxOPTModel
 
 [[autodoc]] FlaxOPTModel