Automate redeployments with GitHub Actions

Changes to the pygeoapi GitHub repo are automatically propagated via DockerHub and a DockerHub listener here.

But changes to the `demo.pygeoapi.io` repo like config or data changes here are not auto-deployed.
[Manual action via Ansible](https://github.com/geopython/demo.pygeoapi.io/tree/master/ansible) is required like:

`ansible-playbook -vv deploy.yml -i hosts/demo.pygeoapi.io --tags update,pygeoapi_master` etc

Also one needs SSH access.

To have full CI deployment GitHub Actions need to be developed such that anyone with commit rights to the demo repo here can redeploy a service.

Hint: there are quite some GH Actions Ansible modules available, the commands are simple enough, SSH-keying may be the biggest challenge, docs:

* https://misfra.me/2019/10/using-ansible-with-github-actions/ - seems simplest solution
* [extensive article on Medium](https://medium.com/swlh/deploying-docker-compose-applications-with-ansible-and-github-actions-7f1740392507)