Include the other interface configs from /etc/network/interfaces.d/ after lo
and existing eth*, as was initially intended.
Also separate out the assembly code into its own script, as this is done both
on boot via eth-eni-setup and on hotplug events by etc-eni-hotplug.
Resolves#91
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)
