* Added new docker tag variations to specify the debian version ('stretch', and 'buster').
* Arch images are alway as specific as possible: pihole/pihole:master-amd64-stretch
* Multiarch images have both the specific debian version tags as well as the generic non-debian tags: pihole/pihole:master-stretch & pihole/pihole:master
* Currently, the non-specific tags point to the 'stretch' images. Eventaully it can be migrated to 'buster'.
* Use GitHub actions to do the builds. Although the script names include 'gh-actions' to differentiate them from the 'circle' scripts, there is zero logic that is specific to Github (ie. no Github environment variables).
* 'armhf:buster' & 'arm64:buster' has an issue with `ip route get`. I think the issue is related to 'qemu', but I'm not sure. Update the `validate_env` function to only use `ip route get` if `nc` reports something strange.
Signed-off-by: Daniel <daniel@developerdan.com>
Daniel