Updates:
* Alpine to 3.14.3
* Debian to 11.1
* binfmt to tonistiigi/binfmt:qemu-v6.1.0 (required for building Debian 11 ARM images with buildx)
Furthermore the [pushrm](https://github.com/christian-korneck/docker-pushrm) Docker CLI plugin is now used for updating the README on Docker Hub.
Signed-off-by: Wouter Born <github@maindrain.net>
* Make Dockerfiles more generic so they can be reused for all openHAB versions
* Determine version information automatically based on openhab-distro tags/branches
* Merge helper scripts into helper-functions
* Add "build" script to simplify building multiple versions or a specific distro using BuildKit
* Add GitHub Actions workflows for PR builds
Fixes#318
Signed-off-by: Wouter Born <github@maindrain.net>