dalle mega
# What does this PR do?

This PR adds the DalleMega model from [dalle-mini](https://github.com/borisdayma/dalle-mini) for text-2-image generation.
The VQGAN model required for converting the tokens to image is in this PR #18150

- [ ] override the `sample` method for classifier-free guidance. 
- [ ] port and upload weights on the hub
- [ ] add tests
- [ ] add docs
- [ ] boom!
@patil-suraj - I can take over the PR if you want :-)<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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