[docs] update input documentation for MAMBA2 and MISTRAL models to include cache_position and attention_mask details
Author: h3110Fr13nd
Pull request: yes

# What does this PR do?
Mamba2 and Mistral models had Input docstrings not exactly matching with forwrd pass of their respective models.
This doesn't have a big impact.
But I'm trying to add modular models. Which I'm subclassing from Mistral.  https://github.com/huggingface/transformers/issues/33916
And documentation mismatch is somehow  not overriding. Which seems to be a lacking in Mistral model.


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Comments:
Also, in `modelling_mistral.py` there's a typo in input docstring

```diff
attention_mask
              ...
-            If `past_key_values` is used, optionally only the last `decoder_input_ids` have to be input (see
+            If `past_key_values` is used, optionally only the last `input_ids` have to be input (see
            `past_key_values`).
```

as suggested by docs of past_key_values and the forward args
```python
past_key_values
            ...
            If `past_key_values` are used, the user can optionally input only the last `input_ids` (those that don't
            have their past key value states given to this model) of shape `(batch_size, 1)` instead of all `input_ids`
            of shape `(batch_size, sequence_length)`.
```
@stevhliu 

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