Mixed CPU/GPU generation on 2.2

Hello!
This is not actually an issue, but a kind of a "how-to" post, namely how to use the model on a lower-end GPUs. The way proposed here is to generate embeddings on the CPU, convert them from float32 to float16 and run the decoder on the GPU.
This way, one can generate images as large as 1024x1024 (the largest "officially supported" size) on a 8GB GPU. On my PC (Ryzen9 3950x CPU + RTX 2080 Super GPU) the speed is about 50 seconds per 1024x1024 image (note that the embeddings probably can be generated in a single batch, but I didn't yet figured out how to pass them separately, since the "plain" indexing does not work). *(Note that the 2.1 was uncapable to generate even 768x768 on the same GPU.)*

The code (plain old `.py` script, but can be easily converted to a `.ipynb` notebook):
```python
import sys
from diffusers import KandinskyV22Pipeline, KandinskyV22PriorPipeline
import torch
import PIL
import os
from diffusers.utils import load_image
from torchvision import transforms
from transformers import CLIPVisionModelWithProjection
from diffusers.models import UNet2DConditionModel
from uuid import uuid4
import numpy as np

DEVICE_CPU = torch.device('cpu:0')
DEVICE_GPU = torch.device('cuda:0')

# Loading encoder and prior pipeline into the RAM to be run on the CPU
# and unet and decoder to the VRAM to be run on the GPU.
# Note the usage of float32 for the CPU and float16 (half) for the GPU
# Set the `local_files_only` to True after the initial downloading
# to allow offline use (without active Internet connection)
print("*** Loading encoder ***")
image_encoder = CLIPVisionModelWithProjection.from_pretrained(
'kandinsky-community/kandinsky-2-2-prior',
subfolder='image_encoder',
cache_dir='./kand22',
# local_files_only=True
).to(DEVICE_CPU)

print("*** Loading unet ***")
unet = UNet2DConditionModel.from_pretrained(
'kandinsky-community/kandinsky-2-2-decoder',
subfolder='unet',
cache_dir='./kand22',
# local_files_only=True
).half().to(DEVICE_GPU)

print("*** Loading prior ***")
prior = KandinskyV22PriorPipeline.from_pretrained(
'kandinsky-community/kandinsky-2-2-prior',
image_encoder=image_encoder,
torch_dtype=torch.float32,
cache_dir='./kand22',
# local_files_only=True
).to(DEVICE_CPU)

print("*** Loading decoder ***")
decoder = KandinskyV22Pipeline.from_pretrained(
'kandinsky-community/kandinsky-2-2-decoder',
unet=unet,
torch_dtype=torch.float16,
cache_dir='./kand22',
# local_files_only=True
).to(DEVICE_GPU)

job_id = str(uuid4())

# torch.manual_seed(42)

num_batches = 4
images_per_batch = 1
total_num_images = images_per_batch * num_batches

negative_prior_prompt = 'lowres, text, error, cropped, worst quality, low quality, jpeg artifacts, ugly, duplicate, morbid, mutilated, out of frame, extra fingers, mutated hands, poorly drawn hands, poorly drawn face, mutation, deformed, blurry, dehydrated, bad anatomy, bad proportions, extra limbs, cloned face, disfigured, gross proportions, malformed limbs, missing arms, missing legs, extra arms, extra legs, fused fingers, too many fingers, long neck, username, watermark, signature'

images = []

print(f"*** Generating {total_num_images} image(s) ***")
for i in range(num_batches):
print(f"* Batch {i + 1} of {num_batches} *")

# Generating embeddings on the CPU
img_emb = prior(
prompt='Feline robot, 4k photo',
num_inference_steps=25,
num_images_per_prompt=images_per_batch)

negative_emb = prior(
prompt=negative_prior_prompt,
num_inference_steps=25,
num_images_per_prompt=images_per_batch
)

# Converting fp32 to fp16, to run decoder on the GPU
image_batch = decoder(
image_embeds=img_emb.image_embeds.half(),
negative_image_embeds=negative_emb.image_embeds.half(),
num_inference_steps=25, height=1024, width=1024)

images += image_batch.images

# Saving the images
os.mkdir(job_id)
for (idx, img) in enumerate(images):
img.save(f"{job_id}/img_{job_id}_{idx + 1}.png")
```