[`IDEFICS`] Fix idefics config refactor
# What does this PR do?

Refactors the `IdeficsConfig` to match the configuration composition patterns of multimodal models on transformers

original PR: https://github.com/huggingface/transformers/pull/24796 

Summary of the changes

- Removed the copy of `CLIPTextConfig`, `CLIPConfig` in `clip.py` as they were used for type hints only
- Retrieve the correct attributes on `modeling_idefics.py` (i.e. attributes from `perceiver_config` & `vision_config`
- Adapted CI tests accordingly
- Make the `utils/check_config_attributes.py` pass - since there is a duplicated CLIPVisionConfig (1 in the clip itself and the other in `configuration_idefics.py`), that script checks the unused attributes of that config for some reason (didn't 
investigated further)

For compatiblity with weights on the Hub, changes similar than: https://huggingface.co/HuggingFaceM4/tiny-random-idefics/discussions/3 needs to be applied

The docstring of the new config objects needs to be cleaned up, but can be done on the main PR.

cc @stas00
_The documentation is not available anymore as the PR was closed or merged._