[Advanced DreamBooth LoRA SDXL] Support EDM-style training (follow up of #7126) (#7182)
* add edm style training
* style
* finish adding edm training feature
* import fix
* fix latents mean
* minor adjustments
* add edm to readme
* style
* fix autocast and scheduler config issues when using edm
* style
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Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>