Support pathlib.Path for input_file_list

[hombit]

Currently, if I pass a list of pathlib.Path objects into ImportArguments(input_file_list=), the processing runs well until "Finishing" step. At this step metadata creation fails when trying to dump json, saying that PosixPath is not serialiasable. Since stdlib's pathlib.Path is a modern and convenient way of path manipulations, I believe we should support it.

File ~/.virtualenvs/hipscat-import-sfd/lib/python3.11/site-packages/hipscat/io/write_metadata.py:27, in write_json_file(metadata_dictionary, file_pointer, storage_options)
     15 def write_json_file(
     16     metadata_dictionary: dict,
     17     file_pointer: file_io.FilePointer,
     18     storage_options: Union[Dict[Any, Any], None] = None,
     19 ):
     20     """Convert metadata_dictionary to a json string and print to file.
     21 
     22     Args:
   (...)
     25         storage_options: dictionary that contains abstract filesystem credentials
     26     """
---> 27     dumped_metadata = json.dumps(metadata_dictionary, indent=4)
     28     file_io.write_string_to_file(file_pointer, dumped_metadata + "\n", storage_options=storage_options)

TypeError: Object of type PosixPath is not JSON serializable