add_text2video_pipeline

[naomili0924]

What does this PR do?

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

[IlyasMoutawwakil]

@naomili0924 thanks for updating this function (this also answers my question in huggingface/optimum-onnx#105 (review))
I think we should rather have everything in optimum-onnx, the same way we did with sana, i.e. create a custom function for splitting wan pipelines in optimum-onnx, this function is becoming more and more complicated as it tries to handle all kinds of pipelines which makes it too complex.