Set up IT/UI tests against real AEM with GitHub Actions

[kwin]

The approach from orbinson/aem-dictionary-translator#73 could be leveraged, i.e. putting a docker image inside the GitHub Container registry which contains AEM 6.5/AEMaaCS SDK. Then this container could be used inside GitHub Actions as outlined in https://docs.github.com/en/actions/use-cases-and-examples/using-containerized-services/about-service-containers.