CogVideo cog

This fork builds a Replicate cog for CogVideo, available as a demo: https://replicate.com/nightmareai/cogvideo

Please see the official repo for more information on CogVideo: https://github.com/THUDM/CogVideo

The pipeline code has been refactored into predict.py, no significant changes were made beyond making the DSR step optional.