Move Wuerstchen Dreambooth to research_projects

[ParagEkbote]

As discussed in #6247, I have moved the files to the requested folder to close the mentioned PR.

Please let me know if any improvements are needed and I will make the necessary changes.

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cc: @sayakpaul

[HuggingFaceDocBuilderDev]

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[sayakpaul]

Thanks! Merging as Kashif has already approved.