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)
Profiles can specify 'setup_script' to do additional things. If additional files/dirs are required, a 'setup_copy' map will copy them to the build instance so that 'setup_script' can use/install them.
TBD: docs.
* Build Profiles (completion of PR #49)
+ auto-updates version profile when new release detected
+ updates releases/<profile>.yaml after successful builds
* Prune AMIs (in AWS and in releases/<profile>.yaml
+ 'revision' - keep latest revision per release
+ 'release' - keep latest release per version
+ 'version' - remove end-of-life versions
* releases/README.md updater script
* README overhaul
+ Pre-built AMIs --> releases/README.md
+ profiles/README.md for profile configuration details
+ main README.md overhauled to go over how to build and manage custom AMIs
