adding callback_on_step_end for StableDiffusionLDM3DPipeline

[rootonchair]

What does this PR do?

Fixes #7136

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[rootonchair]

Test script

import torch
from diffusers import StableDiffusionLDM3DPipeline

def callback_dynamic_cfg(pipe, step_index, timestep, callback_kwargs):
    # adjust the batch_size of prompt_embeds according to guidance_scale
    if step_index == int(pipe.num_timesteps * 0.4):
        prompt_embeds = callback_kwargs["prompt_embeds"]
        prompt_embeds = prompt_embeds.chunk(2)[-1]

        # update guidance_scale and prompt_embeds
        pipe._guidance_scale = 0.0
        callback_kwargs["prompt_embeds"] = prompt_embeds
    return callback_kwargs

pipe = StableDiffusionLDM3DPipeline.from_pretrained("Intel/ldm3d-4c")
pipe = pipe.to("cuda")

prompt = "a photo of an astronaut riding a horse on mars"
generator = torch.Generator()
generator.manual_seed(42)
output = pipe(prompt, generator=generator, callback_on_step_end=callback_dynamic_cfg, callback_on_step_end_tensor_inputs=['prompt_embeds'])
rgb_image, depth_image = output.rgb, output.depth
rgb_image[0].save("astronaut_ldm3d_rgb.jpg")
depth_image[0].save("astronaut_ldm3d_depth.png")

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[yiyixuxu]

looking great! thanks!
think we are just missing some #copied from

[yiyixuxu]

add #copied from?

[yiyixuxu]

add a #Copied from

[rootonchair]

Sure, I will