[Feature] Support Idefics2 models

### Motivation

Extend lmdeploy supported multimodal models to include idefics2 architecture

### Related resources

- [Huggingface official documentation](https://huggingface.co/docs/transformers/main/en/model_doc/idefics2)
- [Huggingface Model Repo](https://huggingface.co/HuggingFaceM4/idefics2-8b)
- [Huggingface Trnasformers Implementation](https://github.com/huggingface/transformers/tree/main/src/transformers/models/idefics2)

### Additional context

_No response_

Start with the Hugging Face Idefics2 documentation, the HuggingFaceM4/idefics2-8b model repository, and the linked Transformers implementation to understand the architecture and expected inputs. Then locate the corresponding multimodal model entry points in lmdeploy; done means Idefics2 is supported by the toolkit.

Written by the indexing model from the issue text.