InstructPix2Pix training script for SD3

**Is your feature request related to a problem? Please describe.**
It would be awesome to see a training script for InstructPix2Pix based on Stable Diffusion 3 such as [this](https://github.com/huggingface/diffusers/blob/main/examples/instruct_pix2pix/train_instruct_pix2pix_sdxl.py).

**Describe the solution you'd like.**
A training script for IP2P based on SD3.

**Describe alternatives you've considered.**
None

**Additional context.**
None

Start by reading examples/instruct_pix2pix/train_instruct_pix2pix_sdxl.py, which is provided as the reference implementation. Determine how its InstructPix2Pix training flow should correspond to Stable Diffusion 3, then add the requested SD3-based training script and verify that it supports IP2P training.

索引モデルが issue の本文から書いたものです。