add ltx2 vae in sana-video; (#13229)
* add ltx2 vae in sana-video;
* add ltx vae in conversion script;
* Update src/diffusers/pipelines/sana_video/pipeline_sana_video.py
Co-authored-by: YiYi Xu <yixu310@gmail.com>
* Update src/diffusers/pipelines/sana_video/pipeline_sana_video.py
Co-authored-by: YiYi Xu <yixu310@gmail.com>
* condition `vae_scale_factor_xxx` related settings on VAE types;
* make the mean/std depends on vae class;
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Co-authored-by: YiYi Xu <yixu310@gmail.com>
