Add seed choose

[Drovosek01]

Using app DownloadFullInstaller - https://github.com/perez987/DownloadFullInstaller

We can switch between several "download seeds"

Please add this funtion to the script

[gregneagle]

It has existed for years. See the --seedprogram option. installinstallmacos.py --help will show you the available options.