Auto-add timm tag to timm-wrapper models. (#35794)

Works for fine-tuned or exported models:

```py
from transformers import AutoModelForImageClassification

checkpoint = "timm/vit_base_patch16_224.augreg2_in21k_ft_in1k"
model = AutoModelForImageClassification.from_pretrained(checkpoint)

model.push_to_hub("pcuenq/tw1")
```

The uploaded model will now show snippets for both the timm and the
transformers libraries.

src/transformers/models/timm_wrapper/modeling_timm_wrapper.py

@@ -81,6 +81,7 @@ class TimmWrapperPreTrainedModel(PreTrainedModel):
     main_input_name = "pixel_values"
     config_class = TimmWrapperConfig
     _no_split_modules = []
+    model_tags = ["timm"]
 
     # used in Trainer to avoid passing `loss_kwargs` to model forward
     accepts_loss_kwargs = False