Add GitHub Actions workflow for publishing Docker container

[andycottonpih]

The PR adds a manual action to publish partnersinhealth/openmrs-distro-zl:latest to dockerhub. We will need to create this repository, and create appropriate secrets for the action before publishing. Once the workflow is tested we can add it to the current build chain, or alternately could set a cron to check if the dependency snapshots have been updated.

I don't currently have acess to make the changes on the dockerhub org, I will add dockerhub administration as a post-standup topic.

[mseaton]

Thanks @andycottonpih - let me finish what I am doing with distro-pihsl and get it to you for review and we can iterate on that, and then we can bring back to this project what we learned.

[andycottonpih]

Sounds good, no rush to start publishing currently, just wanted to get an initial build step into a PR to include in the next docker discussion. I'll mark this as a draft for now.