What does this PR do?

The original notebook doesn't work out of the box. After the following fixes, it works. Fixes

updated diffusers[training] version to the 0.27.2
fixed "TODO" in one of the cells by adding a missing link to another notebook with Unconditional image generation
changed logging_dir to project_dir, because that was a reason for the error (this is also mentioned here: https://github.com/huggingface/notebooks/pull/412)
added the create_repo function for the creation of a repository for the model save if we choose to upload the model to the Hugging Face Hub. Before that, it caused an error during repository pulling

Who can review?

@anton-l