[CvT] Tensorflow implementation (#18597)

* implemented TFCvtModel and TFCvtForImageClassification and modified relevant files, added an exception in convert_tf_weight_name_to_pt_weight_name, added quick testing file to compare with pytorch model

* added docstring + testing file in transformers testing suite

* added test in testing file, modified docs to pass repo-consistency, passed formatting test

* refactoring + passing all test

* small refacto, removing unwanted comments

* improved testing config

* corrected import error

* modified acces to pretrained model archive list, to pass tf_test

* corrected import structure in init files

* modified testing for keras_fit with cpu

* correcting PR issues + Refactoring

* Refactoring : improving readability and reducing the number of permutations

* corrected momentum value + cls_token initialization

* removed from_pt as weights were added to the hub

* Update tests/models/cvt/test_modeling_tf_cvt.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

docs/source/en/model_doc/cvt.mdx

@@ -51,3 +51,14 @@ This model was contributed by [anugunj](https://huggingface.co/anugunj). The ori
 
 [[autodoc]] CvtForImageClassification
     - forward
+
+## TFCvtModel
+
+[[autodoc]] TFCvtModel
+    - call
+
+## TFCvtForImageClassification
+
+[[autodoc]] TFCvtForImageClassification
+    - call
+