convert : add --print-supported-models option

This commit adds a new option to the convert_hf_to_gguf.py script to
print the supported models.

The motivation for this is that it can be useful to know which models
are supported by the script without having to look at the code.

Example usage:
```console
$ ./convert_hf_to_gguf.py --print-supported-models
Supported models:
- GPTNeoXForCausalLM
- BloomForCausalLM
- BloomModel
- MPTForCausalLM
- OrionForCausalLM
- BaichuanForCausalLM
- BaiChuanForCausalLM
- XverseForCausalLM
- FalconForCausalLM
- RWForCausalLM
- GPTBigCodeForCausalLM
- GPTRefactForCausalLM
- StableLmForCausalLM
- StableLMEpochForCausalLM
- LlavaStableLMEpochForCausalLM
- LLaMAForCausalLM
- LlamaForCausalLM
- MistralForCausalLM
- MixtralForCausalLM
- DeciLMForCausalLM
- BitnetForCausalLM
- GrokForCausalLM
- DbrxForCausalLM
- MiniCPMForCausalLM
- MiniCPM3ForCausalLM
- QWenLMHeadModel
- Qwen2ForCausalLM
- Qwen2VLForConditionalGeneration
- WavTokenizerDec
- Qwen2MoeForCausalLM
- GPT2LMHeadModel
- PhiForCausalLM
- Phi3ForCausalLM
- PhiMoEForCausalLM
- PlamoForCausalLM
- CodeShellForCausalLM
- InternLM2ForCausalLM
- BertModel
- BertForMaskedLM
- CamembertModel
- RobertaModel
- NomicBertModel
- XLMRobertaModel
- XLMRobertaForSequenceClassification
- GemmaForCausalLM
- Gemma2ForCausalLM
- Starcoder2ForCausalLM
- Rwkv6ForCausalLM
- RWKV6Qwen2ForCausalLM
- MambaForCausalLM
- MambaLMHeadModel
- FalconMambaForCausalLM
- CohereForCausalLM
- Cohere2ForCausalLM
- OLMoForCausalLM
- OlmoForCausalLM
- Olmo2ForCausalLM
- OlmoeForCausalLM
- JinaBertModel
- JinaBertForMaskedLM
- OpenELMForCausalLM
- ArcticForCausalLM
- DeepseekForCausalLM
- DeepseekV3ForCausalLM
- DeepseekV2ForCausalLM
- UMT5ForConditionalGeneration
- MT5ForConditionalGeneration
- T5ForConditionalGeneration
- T5WithLMHeadModel
- T5EncoderModel
- JAISLMHeadModel
- ChatGLMModel
- ChatGLMForConditionalGeneration
- NemotronForCausalLM
- ExaoneForCausalLM
- GraniteForCausalLM
- GraniteMoeForCausalLM
- ChameleonForCausalLM
- ChameleonForConditionalGeneration
```

convert_hf_to_gguf.py

@@ -478,6 +478,11 @@ class Model:
             return modelcls
         return func
 
+    @classmethod
+    def print_registered_models(cls):
+        for name in cls._model_classes.keys():
+            print(f"- {name}")
+
     @classmethod
     def from_model_architecture(cls, arch: str) -> type[Model]:
         try:
@@ -4929,6 +4934,7 @@ def parse_args() -> argparse.Namespace:
     parser.add_argument(
         "model", type=Path,
         help="directory containing model file",
+        nargs="?",
     )
     parser.add_argument(
         "--use-temp-file", action="store_true",
@@ -4966,8 +4972,15 @@ def parse_args() -> argparse.Namespace:
         "--metadata", type=Path,
         help="Specify the path for an authorship metadata override file"
     )
+    parser.add_argument(
+        "--print-supported-models", action="store_true",
+        help="Print the supported models"
+    )
 
-    return parser.parse_args()
+    args = parser.parse_args()
+    if not args.print_supported_models and args.model is None:
+        parser.error("the following arguments are required: model")
+    return args
 
 
 def split_str_to_n_bytes(split_str: str) -> int:
@@ -4991,6 +5004,11 @@ def split_str_to_n_bytes(split_str: str) -> int:
 def main() -> None:
     args = parse_args()
 
+    if args.print_supported_models:
+        print("Supported models:")
+        Model.print_registered_models()
+        sys.exit(0)
+
     if args.verbose:
         logging.basicConfig(level=logging.DEBUG)
     else: