Update model type (WIP)

`maest` (Music Audio Spectrogram Transformer) is a variant of AST featuring the same architecture but a different mel-spectrogram configuration optimized for music applications.

config.json

@@ -815,7 +815,7 @@
   },
   "layer_norm_eps": 1e-06,
   "max_length": 1876,
-  "model_type": "audio-spectrogram-transformer",
+  "model_type": "maest",
   "num_attention_heads": 12,
   "num_hidden_layers": 12,
   "num_mel_bins": 96,