Bring Docker image for avatica-standalone-server into Apache

I worked on making some Docker images for the standalone Avatica Server with HSQLDB.

https://hub.docker.com/r/joshelser/avatica-hsqldb/

These greatly simplify running the Avatica TCK and also provide a portable server that developers can use when testing custom Avatica clients.

For >=1.9.0, we should an image into Avatica (upstream). There are a couple of open questions on my mind already:

1. What are the release-ability concerns (do we provide SNAPSHOT Dockerfiles but not built images as they may be interpreted as "releases")?
2. What ASF integrations exist (do we need to ask Infra for things?)
3. Are there any maven plugins we should consider for automation? (https://github.com/spotify/docker-maven-plugin)