feat: GitHub Action for automated testing

[carlomion]

I was made aware of this project by a discussion on mediagis/nominatim-docker#470.
Firstly, thank you for your effort! I greatly appreciate the approach of separating the various containers, each with a specific purpose.

I would like to ask if there is any plan to introduce GitHub Actions to validate the image building process, checking for instance that the built binary can be correctly executed, or even that the overall stack is able to respond to HTTP requests.

This may be helpful in avoiding regressions with new releases, given that for instance version 4.4 has made the Python API the default frontend, and it might be helpful to introduce support for it here.