`lightning_getattr` should raise `AttributeError`
🚀 Feature Enhancement
Currently, lightning_getattr(model, attribute) raises one of (ValueError, KeyError, AttributeError when attribute is not found in model, but I think it should raise AttributeError in all cases since Python built-in getattr() only raises AttributeError.

  
    
      pytorch-lightning/pytorch_lightning/utilities/parsing.py
    
    
         Line 241
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           def lightning_getattr(model, attribute):