SD3 dreambooth training - caching of embeddings and vae representations

**Is your feature request related to a problem? Please describe.**
The current implementation of the dreambooth trainings for both loras and finetuning is very memory intensive.

**Describe the solution you'd like.**
I would like the option to pre-cache the VAE representations of the images and the text encoder representations so that training could be done without the text encoders being in VRAM.

**Describe alternatives you've considered.**
I don't believe there are alternatives to reducing the VRAM requirement for training.