Support arm64 builds using 'docker buildx'

[dougdonohoe]

Now that Apple M1 (Apple Silicon) Macs are becoming more common, it is desirable to have tools like this support both amd64 and arm64 images. This PR adds a Makefile with the commands necessary to build and publish such an image as well as instructions in the README.

I also bumped Alpine to v3.15 and made it easier to publish a different version of Kafka.

The owner of this repo should be able to publish a multi-arch image:

REPO_NAME=johnnypark make buildx-publish 

I also published my image to https://hub.docker.com/r/dougdonohoe/kafka-zookeeper.

[obalunenko]

Hi @dougdonohoe This repository is not maintained. You can use this one: https://github.com/obalunenko/docker-kafka-zookeeper . It already has pre-build images for all Kafka with zookeeper versions published on the official site https://kafka.apache.org/downloads