[Feat] support AutoPipelineForText2Audio

[RuixiangMa]

What does this PR do?

support AutoPipelineForText2Audio for ext2Audio model

import torch
import soundfile as sf
from diffusers import AutoPipelineForText2Audio

pipeline = AutoPipelineForText2Audio.from_pretrained(
    "stabilityai/stable-audio-open-1.0",
    torch_dtype=torch.float16
)
pipeline = pipeline.to("cuda")

output = pipeline(
    "Generate a male voice reading a paragraph",
    num_inference_steps=20,
    audio_end_in_s=10.0,
)

audio = output.audios[0].T.float().cpu().numpy()
sf.write("audio.wav", audio, pipeline.vae.sampling_rate)

audio.wav

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline?
• Did you read our philosophy doc (important for complex PRs)?
• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.