multistep macos setup
This updates the macOS node setup instructions to avoid repeating
identical work and network traffic across all machines through
initialization by building a "daily" image with all the tools and code
we need.
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* Fix 3-running-box to remount nix partition
* updated scripts to use multi-step process
* add copyright notices
Co-authored-by: nycnewman <edward@digitalasset.com>
