add **encoding** argument in netCDF4 backend

[wqshen]

add encoding argument in netCDF4 backend to support reading NetCDF file with non-ASCII path or filename.

The behavior is consistent with upstream netCDF4 library, default path encoding is set to sys.getdefaultfileencoding() .

• [x] Closes #10357 #8531

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[dcherian]

Nice, can you add a test here please? https://github.com/pydata/xarray/blob/d589df1868b9d6ec197a91da7e3acb8670bb7641/xarray/tests/test_backends.py#L2037

It can simply roundtrip a simple dataset to a file with a filename that doesn't work today.

[kmuehlbauer]

How is this handled in the light of this comment https://github.com/pydata/xarray/issues/9282#issuecomment-2310573129 by @dcherian?

[dcherian]

Hah! Probably good to use filename_encoding since we'll probably to support writing files with such file names.