`OneHotEncoder` takes a categorical column and output a vector column, which stores the category info in binaries.
It should read the category info from the metadata and assign feature names properly in the output column. We need to discuss the default naming scheme and whether we should let it process multiple categorical columns at the same time.
One category (the most frequent one) should be removed from the output to make the output columns linear independent. Or this could be an option tuned on by default.