Allow auth explicit configuration in task options.

I know this could lead to a security risk if committed into source control. That's why I've added to the documentation a warning about it.

The reason I needed this is because I have some other sensitive information I don't want to put into source control, and I didn't want to have 2 separate files (.ftppass and my other file). Now I can put all my auth configs in one file, and then pass the ftp user/pass via the task options.