Legacy 3. Downloading (caching) a macOS installer pkg

For obtaining installers for macOS 11 Big Sur or greater, experimental support is included for downloading a macOS Installer pkg. This is taken from Armin Briegel's adaptation of installinstallmacos.py at scriptingosx/fetch-installer-pkg.

The installer packages are slightly smaller than the installer applications, and do not need to be compressed into a sparseimage. Therefore, you might be able to slightly speed up the workflow using this option.

Use the --pkg option to download a package. This can be used in conjunction with --list and --move.

When used in conjunction with --list, the available package installers are shown. Using --seedprogram may give access to beta package installers.

When used in conjunction with --move, the package is extracted, so that you end up with a standard Install macOS application in /Applications.

The obtained packages can be used in both --erase and --reinstall workflows. If not already done so, the package is extracted prior to startosinstall running, so you end up with a standard Install macOS application in /Applications.