Option to set "Content-Disposition" HTTP header value

Problem/Motivation

Chrome and Firefox download a CSV file as-is, but Safari instead prints the CSV data directly to the browser window. By setting the Content-Disposition HTTP header, we can force Safari to download the file. This would be good practice regardless.

See: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Dispos...

Proposed resolution

CSV Serialization should provide an option to set the Content-Disposition HTTP header to "inline" or "attachment". It should probably default to "attachment".