Custom filenames upon upload

[JR-1991]

This PR adds the ability to specify a different file name within a File object to be displayed at a Dataverse instance. This is independent of the actual file name found in filepath and overrides the default to use the base name of the latter.

Example

import dvuploader as dv

files = [
    dv.File(
        filepath="test.py",
        file_name="this_is_different.py",
    ),
]

Upon upload, the file test.py will be displayed at Dataverse as this_is_different.py.

Closes #14