Upgrade to the latest macOS version

Works to erase Macs running macOS versions v10.13 High Sierra and newer and up to macOS v11.x Big Sur.

Uses erase-install.sh --update to fetch latest macOS version to install with rather than keeping the same major version using --sameOS.

Includes release 0.19.0 of erase-install.sh. For Silicon Macs, this version ensures the authorising account for startosinstall --eraseinstall is admin. Also running diskutil apfs updatePreboot for Silicon Macs is handled there instead of in the auto-erase-install wrapper script.

Building customised / forked versions is made easier with the automated build.zsh script, now in its first working version.

--sameOS

Automatic download and erase-install of SAME major OS version, no upgrading to latest macOS.

Does NOT ensure if user logged in at console is admin on Apple Silicon M1 Macs, this is not needed on Intel Macs, but appears to be on M1's.