integrate NetCDF compression

integrate NetCDF compression in the in the FTP Operations, before the md5 creation and transfer to PD (in transfer.py#L37 )

This is the function used in disdroDL modules/classes.py

    def compress_netcdf(self):        
        subprocess.run(['nccopy', '-d6', self.path_netCDF, self.path_netCDF_temp])
        self.logger.info(msg=f'Compressed netCDF {self.path_netCDF}')
        os.remove(self.path_netCDF)
        os.rename(self.path_netCDF_temp, self.path_netCDF)