Update pipeline_animatediff.py to add fromsinglefile to pipeline

[chaowenguo]

What does this PR do?

add fromsinglefile to pipeline

Fixes # (issue)

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Who can review?

@hlky

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[hlky]

@chaowenguo Can you share example usage

[chaowenguo]

i need to use The from_single_file() method

[hlky]

@chaowenguo

Fill in the checkpoint I can use to test this.

import torch
from diffusers import AnimateDiffPipeline
from huggingface_hub import hf_hub_download

checkpoint = hf_hub_download(repo_id="", filename="")

pipe = AnimateDiffPipeline.from_single_file(checkpoint)

[chaowenguo]

@hlky

from diffusers import AnimateDiffPipeline

pipe = AnimateDiffPipeline.from_single_file('https://huggingface.co/chaowenguo/pal/blob/main/chilloutMix-Ni.safetensors')