release alpine-ami-3.12.1-aarch64-r1
Also...
* release new edge builds
* Alpine 3.9 is EOL
* build_instance_type set in profiles/arch/
* a couple comment fixes
* eth-eni-setup init script
before networking starts up, makes sure eth interfaces match attached ENIs
also fixes a permissions problem with eth-eni-hotplug mdev config
* fix aarch64 build
ENI Hotplug / udhcpc script
* works with all Alpine versions back to 3.9
* udhcpc handles ENI's primary IPv4
* post-bound/post-renews eth-eni-hook handles secondary IPv4 & IPv6 addresses, route tables, and rules
setup-ami tweaks
* move scripts to be installed into setup-ami.d/
* move config snippets into setup-ami.d/etc/ (previously embedded in setup-ami)
