add from_single_file to animatediff

[ghost]

What does this PR do?

from_single_file can be test with:

motion_adapter = diffusers.MotionAdapter.from_pretrained('chaowenguo/AnimateLCM', torch_dtype=torch.float16, variant='fp16', use_safetensors=True)
pipe = diffusers.AnimateDiffPipeline.from_single_file('https://huggingface.co/chaowenguo/pal/blob/main/chilloutMix-Ni.safetensors', config='chaowenguo/stable-diffusion-v1-5', safety_checker=None, use_safetensors=True, torch_dtype=torch.float16, motion_adapter=motion_adapter)

Fixes # (issue)

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