convert : add --print-supported-models option (#11172)

convert : add --print-supported-models option (#11172)

* 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
```

* squash! convert : add --print-supported-models option

Fix flake8 error.