Publish to Docker Hub automatically

[pradtke]

Automate

• building multi-arch image
• some level of validation of image, perhaps based on the examples in the README
• generation of short lived tls certs/key
• tag and publish to docker hub

[dnmvisser]

Looks like this happened already?

https://hub.docker.com/r/cirrusid/simplesamlphp

[pradtke]

yeah, I've changed this to say automatically