dask_cudf.read_csv doesn't support StringIO

[kijeungchoi]

dask_cudf.read_csv() is calling cudf.read_csv() internally.
However, dask_cudf.read_csv() doesn't support StringIO input.

Description of api mislead (it seems copied over from cudf.read_csv())

    path : str, path object, or file-like object
        Either a path to a file (a str, pathlib.Path, or
        py._path.local.LocalPath), URL (including http, ftp, and S3 locations),
        or any object with a read() method (such as builtin open() file
        handler function or StringIO).

Currently, StringIO input falls into https://github.com/rapidsai/cudf/blob/branch-23.04/python/dask_cudf/dask_cudf/io/csv.py#L99

[GregoryKimball]

Thank you @kijeungchoi for raising this, we will look into updating the docs or adding this feature.