Add additional_startos_options

[apizz]

Currently, additional_startos_options is not available in the pkginfo properties menu.

I'm not sure how it would best to implement this, but given there are a set list of startos options, maybe there could be a dropdown list of arguments which when selected would allow you to add additional options (+ / -) as needed.

Any options that required additional text entry as part of the argument (ex. --newvolumename "Macintosh HD") might have a text entry field adjacent to the parameter.