restore original model_index.json after save_pretrained call

[eaidova]

What does this PR do?

due to registration ov diffusion pipeline components in pipeline config, their classes appears in model_index.json
after OVDiffusionPipeline.save_pretrained().

>>from optimum.intel.openvino import OVDiffusionPipeline

>>pipe = OVPipelineForText2Image.from_pretrained("hf-internal-testing/tiny-stable-diffusion-pipe-variants-right-format")
>>pipe.config
FrozenDict([('vae', ('optimum.intel.openvino.modeling_diffusion', 'OVModelVae')), ('text_encoder', ('optimum.intel.openvino.modeling_diffusion', 'OVModelTextEncoder')), ('tokenizer', ('transformers', 'CLIPTokenizer')), ('unet', ('optimum.intel.openvino.modeling_diffusion', 'OVModelUnet')), ('scheduler', ('diffusers', 'DDIMScheduler')), ('safety_checker', (None, None)), ('feature_extractor', ('transformers', 'CLIPFeatureExtractor')), ('image_encoder', (None, None)), ('requires_safety_checker', True), ('_name_or_path', '/tmp/tmpxgc_1oo1')]

That may bring some inconvinience:

• misalignment between optimum-cli result (cli tool preserves original model_index.json) and save_pretrained results
• impossibility store original and ov pipeline in the same local directory or hub repository. if ov pipeline will be saved vi save_pretrained after original pipeline, you will not able to use original pipeline (model index json will contains wrong class names):

from diffusers import DiffusionPipeline
from optimum.intel.openvino import OVDiffusionPipeline

save_dir = "common_repo"
model_id = "hf-internal-testing/tiny-stable-diffusion-pipe-variants-right-format"
pipe = DiffusionPipeline.from_pretrained(model_id)
pipe.save_pretrained(save_dir)

ov_pipe = OVDiffusionPipeline.from_pretrained(model_id)
ov_pipe.save_pretrained(save_dir)

# try to load original pipeline again
pipe_from_local_dir = DiffusionPipeline.from_pretrained(save_dir)

raises error:

diffusers/utils/import_utils.py", line 846, in __getattr__
    raise AttributeError(f"module {self.__name__} has no attribute {name}")
AttributeError: module diffusers has no attribute OVStableDiffusionPipeline

[HuggingFaceDocBuilderDev]

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