Migrate optuna/notebooks/jupytercon_demo/RAPIDS_xfeat_Optuna-GPU.ipynb to deployment docs

[jacobtomlinson]

Migrate optuna/notebooks/jupytercon_demo/RAPIDS_xfeat_Optuna-GPU.ipynb to deployment docs.

See #203 (comment) for detailed migration instructions.

Tasks

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1. Decide if notebook should be migrated and add "migrate: X" label (if no also close this issue)
2. Test if notebook works
3. Fix up anything that needs changing
4. Ensure notebook has good title, description and metadata tags in the first cell
5. Replace deployment instructions with links to docs pages
6. Copy notebook into a new folder into deployment docs examples
7. Copy any supporting files to the folder
8. Add notebook to examples toctree
9. Make PR to deployment docs repo

[betatim]

Based on rapidsai/deployment#141 (comment): maybe don't migrate this notebook. It doesn't demonstrate integration/use of a cloud service provider and is "yet another optuna" example.