Generalize ``get_dummies``

[rjzamora]

• Generalizes get_dummies/GetDummies to work with cudf
• Fixes a minor bug (missing "sparse" parameter)

[phofl]

I suppose we can't add a test here?

[rjzamora]

I suppose we can't add a test here?

This is a good question. I updated the test to work with both pandas and cudf.

Not sure if we want to add test coverage for the parameters?

[phofl]

I think that's fine, it would be covered by the gpu ci, correct?

[phofl]

thx

[rjzamora]

it would be covered by the gpu ci, correct?

I'm working on this :)