This Fixes#10339, and allows for automatic building of the Alpine Linux
image, and push to docker-hub.
This will push a "latest-alpine" based on the master branch, a
"develop-alpine" based on the develop branch, and a v##.##.##-alpine
image based on any released version.
`DOCKER_USERNAME` and `DOCKER_ACCESS_TOKEN` do both need
to be added to the repository as secrets.
