support iterative outputs for gradio web ui

[AK391]

iterative outputs is now supported in gradio==3.3, see video for example, using diffusers pipeline so nsfw detected images are a black screen but works otherwise, cc: @altryne @hlky @cobryan05

this is how to do it

ezgif.com-gif-maker.16.mov

import numpy as np
import time
import os


def fake_diffusion(steps):
    for i in range(steps):
        time.sleep(1)
        yield np.random.random((200, 200, 3))
    time.sleep(1)
    yield "cheetah.jpg"

with gr.Blocks() as demo:
    slider = gr.Slider(1, 10, 3)
    button = gr.Button()
    image = gr.Image()
    button.click(fake_diffusion, slider, image)

demo.launch()