Add CLI interface to MDS

[David P]

It would be nice to be able to perform certain MDS tasks via command-line.

Examples:

• Replacing a broken package and quickly rebuilding an installer-image

• CD/CD-style automated builds

  • Placing current macOS installer.app in a directory like ‘mds-installer’ so it can change without moving paths
  • Including variables in volume/workflow names like ${DATE} or ${OS_VER} so daily/monthly/whatever builds can be autogenerated

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