[Docs] Model_doc structure/clarity improvements (#26876)

* first batch of structure improvements for model_docs

* second batch of structure improvements for model_docs

* more structure improvements for model_docs

* more structure improvements for model_docs

* structure improvements for cv model_docs

* more structural refactoring

* addressed feedback about image processors

docs/source/en/model_doc/imagegpt.md

@@ -40,7 +40,7 @@ alt="drawing" width="600"/>
 This model was contributed by [nielsr](https://huggingface.co/nielsr), based on [this issue](https://github.com/openai/image-gpt/issues/7). The original code can be found
 [here](https://github.com/openai/image-gpt).
 
-Tips:
+## Usage tips
 
 - ImageGPT is almost exactly the same as [GPT-2](gpt2), with the exception that a different activation
   function is used (namely "quick gelu"), and the layer normalization layers don't mean center the inputs. ImageGPT
@@ -92,7 +92,6 @@ If you're interested in submitting a resource to be included here, please feel f
 ## ImageGPTFeatureExtractor
 
 [[autodoc]] ImageGPTFeatureExtractor
-
     - __call__
 
 ## ImageGPTImageProcessor
@@ -103,17 +102,14 @@ If you're interested in submitting a resource to be included here, please feel f
 ## ImageGPTModel
 
 [[autodoc]] ImageGPTModel
-
     - forward
 
 ## ImageGPTForCausalImageModeling
 
 [[autodoc]] ImageGPTForCausalImageModeling
-
     - forward
 
 ## ImageGPTForImageClassification
 
 [[autodoc]] ImageGPTForImageClassification
-
     - forward